Vulcan 80C Hammer: Specifications and Information

The Vulcan 80C was the Super-Vulcan counterpart to the Warrington-Vulcan 08, and was one of the more successful differential-acting hammer sizes Vulcan produced.

Specifications are below.

Some photos, job and shop, are shown below.

Some general arrangements, Chicago and Chattanooga, are shown below.

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Raymond 65C Hammer: Specifications and Information

temp65cfIt’s evident that Vulcan had some difficulty in getting the right combination of economy, operating pressure and configuration with its 65C and 65CA hammers.  Did Raymond, which made many of its own designs of Vulcan style hammers, do any better?

Based on its experience with the Vulcan differential hammers, Raymond designed several differential-acting hammers, including its own 80C, the 150C, and this hammer.  A general frontal view is shown at the right; a photo of one in Vulcan’s yard is above.  Raymond made several interesting changes in the hammer design:

  • Different sheave had design.
  • Raymond configured the hammer for 120 psi operating pressure, which was one of Vulcan’s original proposals (the Raymond probably antedates the Vulcan 65C.)
  • Coil springs (later rubber springs) at the top for the hammer extension, or sled, which Raymond always used with its leaders.
  • Male jaws to mate the hammer with the extension (Vulcan later used male jaws for its offshore hammers.)
  • Cables from head to base.  Raymond used a tapered bottom fitting; machining the mating tapered holes in the base was tricky and expensive, as Vulcan found out the hard way when it machined a base for the single-acting Raymond 1-S.
  • Draw bar for the slide bar instead of the hammered keys.
  • Baffle in the cylinder for the exhaust; the ports for exhaust were probably higher than for any other Raymond or Vulcan hammer.
  • Steam chest bushing, which Vulcan adapted and improved upon as a removable liner.
  • Lighter, dished-out pistons for the piston rod.  (Why weight reduction was necessary for a striking part component isn’t quite clear…)

Vulcan acquired a great deal of Raymond engineering and inventory when Raymond finally fell apart in the early 1990’s, and was in the process of incorporating many of Raymond’s changes in its own product line when the company was merged in 1996.

kif_0001_3 2
Another view of the Raymond 65C in Vulcan Foundation Equipment’s Yard.

Specifications for the Raymond 65C are shown below.

raymond-50c-65c-80c-125cx-150c-specifications
Specifications for Raymond Differential Hammers

Vulcan 65C and 65CA Hammers: Specifications and Information

The 65C is the counterpart to the Warrington-Vulcan 06 hammer.  Upsizing single-acting hammers is a fairly straightforward process as long as the frame is capable of withstanding the load.  Doing the same thing with differential-acting hammers such as the 50C is an entirely different matter, as the 65C shows.

Specifications are on the general arrangement above and are also shown below.

Bulletin 70J Specifications

65c general arrangement
An early concept of the 65C hammer. The idea here is that the large bore is increased in size, which would have kept the pressure at 120 psig. Vulcan opted to keep the cylinder the same as the 50C, which forced the operating pressure upwards to 150 psig. That in turn required adding a false head to compensate for the additional upward force on the frame. The false head made the 65C expensive to produce, and the high pressure put it out of reach for many air compressors.

Vulcan eventually addressed these issues with the 65CA; the ad for it from Onshore Tip 61 is shown below.

65ca-ad-for-tip-61
The ad for the Vulcan 65CA, on the back of Vulcan Tip 61, 1 November 1981. This hammer was an 80C with a light ram. The operating pressure was now at 95 psig, well within the reach of available air compressors. The main disadvantage of this is that it requires 26″ jaws; how much of a disadvantage that is depends upon the contractor.

 

Vulcan 50C Hammer: Specifications and Information

Like its Warrington-Vulcan counterpart, the #1, the 50C was a popular hammer and, along with the 80C, comprised a large block of Vulcan’s production of these hammers.  Specifications are below.

Some general arrangements are below.  Note that the hammer in the image above sports a bar-type head while these have a sheave-type head; this is explained here.

Vulcan 50C, driving sheet piling. Vulcan hammers weren’t known to be sheet pile specialists but, as these photos show, they got the job done anyway. As was the case before, an “offshore” type leader was used, where a stub leader was hung from a crane and lowered with the hammer. This is good when the pile is supported at the ground, either by a template or in this case other sheet piles.
Vulcan 50C hammer, installing sheet piling, Chicago, 1974. Note the yellow Decelflo muffler on top of the hammer; this was one of the first uses of the exhaust muffler.
Vulcan 50C driving piles on a batter using swinging leaders, Hudson, OH. Swinging leaders are usually used to drive plumb piles, but in this case the leaders are stabbed in the ground so that the whole assembly can be leaned back. It’s done but requires considerable skill on the part of the contractor.
A concept for the muffer: mount it directly on the back of the hammer, using a bracket integral to the hammer. A special cylinder head would transmit the air from the exhaust to the muffler. Unfortunately the Decelflo program didn’t get far enough for Vulcan to try this concept.

Vulcan 30C Hammer: Specifications and Information

The Vulcan 30C was the differential-acting counterpart to the single-acting #2 hammer.  Specifications are below.

The general arrangements are interesting not just for the 30C but to explain features and variants in the Vulcan product line.

Vulcan-30C-030-CTA
Like parent, like child, but the size is reversed: a Vulcan 030 single-acting offshore hammer and a Super-Vulcan 30C hammer, side by side, at the plant in Chattanooga. Note the constructional similarities.

Vulcan 18C Hammer: Specifications and Information

The 18C is the smallest of the Super-Vulcan hammers, designed to correspond with the Warrington-Vulcan #3.  Specifications for the hammer are below.

Like the #3, the small size made it lose popularity, and it lasted longer in Vulcan’s literature than in active production.

Vulcan #4 Hammer: Specifications and Information

The #4, another one of the early Warrington-Vulcan hammers, was the smallest one designed and produced.  It was referred to as the “Fish Stake” hammer, because, as Vulcan’s literature explained, it was “used for driving fish stakes for pond nets along the shore and in connection with sheeting cap, for small wooden sheeting.”

Specifications for this hammer are below.

Specifications Bulletin 68
Specifications, Vulcan Bulletin 68

It’s interesting to note that the #4 only had upper rubber bumpers; there were no rubber bumpers on the base.  This arrangement was eventually incorporated into the very late Warrington-Vulcan hammers, especially the 5′ stroke hammers like the 506 and 512, in order to strengthen the base.

As was the case before valve liners, the shifting of the cylinder cores necessitated valve settings for each hammer.  This was also true of the #4; an example of this for a contractor in Walkerville, Ontario is shown below.  Walkerville was built as a “model town” around the Canadian Club whisky distillery.  Given the propensity of the owning family for whisky, some return on the investment was appropriate.

#4 sn986 slide bar variations

“C.V.A.” is Campbell V. Adams, Vulcan’s engineer for many years and the designer of the Super-Vulcan hammers.

Concrete Pile Cutter SP-88 Operations Manual

One of the more interesting products that Vulcan spent a great deal of time on but was not able to actively pursue was the concrete pile cutter.  The technology for the cutter was developed by two Soviet institutes: VNIIstroidormash in Moscow and Dalniis in Vladivostok.  How Vulcan obtained the rights to the patent was an interesting process and is described hereAn overview of the technology is here.

Here we link to the operations manual (or “Certificate” as the Russians referred to it.)  We trust that you will find this informative as to the operation of this concrete pile cutter, which (to our knowledge) has not been duplicated elsewhere.

Download the Operations Manual for Reinforced Concrete Pile Head Breaker for Pile Caps, SP-88

pilebver

Hydraulic Vibratory Hammer: the Foster 4200

Background

The Foster hammers are an interesting part of Vulcan’s last years.  The concept was to produce a vibratory hammer under a “private label” arrangement, a novelty for the pile driving equipment industry at the time (although the “Chimag” diesel hammers were a similar concept.)  In the early 1990’s Vulcan produced several vibratory hammers for the sheet pile supplier L.B. Foster, merging Foster’s own exciter technology (which was Japanese in origin) with Vulcan’s power pack improvements after parting ways with HPSI.

The purpose of this article, however, is primarily to discuss hydraulic vibratory hammers with an emphasis on the “hydraulic.”  Pile driving equipment in general and vibratory pile driving equipment in particular poses challenges for the equipment designer and manufacturer.  The emphasis here will be on the hydraulics, which are in some ways typical of mobile hydraulics and in some ways unusual.  We will use the Foster 4200–the largest of the hammers Vulcan produced–as an example.

Basics of Fluid Power

Fluid power is an important component of power transmission for many mechanical applications.  Broadly fluid power can be broken down into two parts: industrial and mobile applications.  The emphasis here will be on the latter.  Most construction machinery manufactured today has some hydraulic control or power included in the equipment.  The original vibratory hammers, designed and produced in the then Soviet Union, were electric, but with the introduction of hydraulic vibratory drivers in the 1960’s today most are hydraulic.

The concept behind fluid power is simple:

  1. A flow of fluid is pressurised.
  2. The fluid is delivered to where it is needed.
  3. The fluid does its work, and is depressurised in the process.
  4. The fluid, at or near atmospheric pressure, returns to where it is pressurised.
  5. The process is repeated.

Since the hydraulic fluid being used (petroleum-based, plant-based, or even water) is virtually incompressible, considerations such as occupy students of thermodynamics are not an issue here, although they appear in other parts of the hydraulic system.  The power being delivered at any point by a fluid power system is the product of pressure and flow, thus

HP=\frac{ PSI \times GPM}{ 1714}

where HP is the horsepower being delivered by the fluid, PSI is the gauge pressure of the fluid in pounds per square inch, and GPM is the flow rate in U.S. gallons per minute.

Both the flow and pressure of the fluid are generally delivered by pumps.  Fluid power is a little different from many pumping applications in that the pumps are almost always positive displacement, to insure the accuracy of the flow and pressure.  The pump performs the first step of the process outlined above; if the power is transmitted at the other end in a rotary way, a motor performs the third step.  Unsurprisingly hydraulic pumps and motors are basically mirror images of each other; their construction is similar (not necessarily identical) and their operation is similar.  There are several types of hydraulic pumps and motors in use; we’ll concentrate on piston motors and pumps for two reasons:

  1. These are what were used in the Foster 4200 and all of Vulcan’s high pressure machinery (more about pressure levels later.)
  2. They’re a little easier to visualise if you’re not familiar with the application.

Let’s look at a cutaway pump/motor.

Piston-Hydraulic-Pumps-1

The large bronze barrel in the centre of the motor has a series of holes in a radial pattern, into which the pistons (those small cylinders with the rounded left ends) are inserted.  The plate an an angle to the bronze barrel is the swash plate, which (through the other plates) either drives (motor) or is driven by (pump) the spline at the left end of the motor, which connects to whatever the motor is driving or the pump is being driven by.  The angle between the barrel and the swash plate alows the pistons to move in the barrel, much like the pistons in an automobile do.  The displacement per piston is given by

DIS = A \times L

where DIS is the displacement of each piston in cu.in., A is the cross-sectional area of the piston in sq.in., and L is the stroke of the piston in the barrel in inches.  The total displacement per revolution of the barrel is obviously

DIS_{tot} = DIS \times N

where DIS_{tot} is the total displacement in one revolution in cu.in./revolution and N is the number of pistons.

The flow of the pump or motor is given by

GPM = \frac {DIS_{tot} \times RPM}{231}

where RPM is the rotational speed of the motor is revolutions/minute.  The horsepower output of the motor (or input of the pump) was given earlier.  The torque of the motor/pump is

T = \frac{5252 \times HP}{RPM}

where T is the torque of the motor or pump in foot-pounds.

The simplest configuration of a pump or motor is a fixed-displacement.  In this the angle between the barrel and the drive spline (or keyway) is fixed and thus the stroke L is fixed.  This precise flow is an important aspect of fluid power systems, as it regulates the speed of the load, which can be rotational or translational.

However, there are good reasons for varying the displacement–and thus the flow output–of a hydraulic pump.  The pump shown above has a mechanism on the right which varies the position of the right end of the barrel, and thus the displacement of the pistons.  Although it’s possible to vary this control manually, the mechanism shown does so by measuring the pressure of the hydraulic fluid, and thus is referred to as pressure-compensated.  We’ll come back to why that’s important later.

One further thing that complicates the equations above is leakage around the pistons.  Because of the speed of their movement, most piston pumps and motors–and for that matter most hydraulic motors, pumps and valves–do not use seals in them, but tightly fit the pistons or valve spools to the barrel or valve body and allow some leakage.  Although this may seem inefficient, the small oil flow allows for lubrication of the components and cooling of the pumps and motors without the drag that seals would induce.  This reduces the flow available for power transmission, and the ratio of the ideal flow to the flow actually available after leakage is referred to as volumetric efficiency.  This can vary for a number of reasons, but for piston motors and pumps such as we are dealing with here a volumetric efficiency of 90% is a good estimate.

Overview of the Foster 4200

A general overview of vibratory hammers, their theory and application, is given in the monograph Vibratory and Impact-Vibration Pile Driving Equipment.  Without going into the detail of that monograph, the following illustrates the basic components of the system.

TEMPMEDV

The exciter does the work of the system by inducing a vertical, sinusoidal force in the pile, which sinks by its own weight.  The eccentrics producing this force are turned by a motor, which is driven by a pump on the power pack through the hoses.  The pump in turn is driven by a diesel engine, which is the prime mover of the system.  There’s also a clamp to hold the driver to the pile; in reality there are two hydraulic systems, one for the motor and one for the clamp.  This allows us to illustrate hydraulic systems with both rotational output (the motor) and translational output through a cylinder (the clamp.)

The exciter for the 4200 is shown below.  If you’re interested in details on this unit, including the specifications, you can download the Foster 4200 Field Service Manual, First and Second Units.

Foster-4200-Exciter

The 4200 has two motors to drive its eight (8) eccentrics, but in this case only one clamp for sheeting.  A hose layout for the exciter is shown below.

4200_1&2_Page_47
The hose layout for the 4200 exciter. There were five hoses going back to the power pack: the supply hose (94), return hose (93), case drain (2), and the two clamp hoses (15).

The supply hose is the hose which carries the pressurised oil to the motors.  The return hose carries the depressurised oil back to the power pack.  The case drain hose returns the leakage from the motor (see earlier comments on volumetric efficiency) back to the power pack.  In some cases the return hose can be used as a case drain hose, but in this application there is too much back pressure.  The two clamp hoses are bi-directional, as we will discuss shortly.

foster pp outside
An outside shot of the power pack. The control panel is for an electric-over-hydraulic system which Vulcan began using when it built its own power packs. The remote control pendant allows the unit to be operated from the crane or wherever is most convenient. The hoses come from the exciter and can be 50′-150′ long for this size of unit. The quick disconnects allow easy connection and disconnection of the hoses from the power pack, but should be avoided when possible because they contribute to frictional losses in the hydraulic fluid.

Until 1991 Vulcan purchased its power packs from HPSI, which used an air-over-hydraulic control system.  In going to electric-over-hydraulic, Vulcan was more in line with its competition such as ICE and APE.

foster pp inside
Looking through the doors of the power pack. The diesel engine is the prime mover of the system. The pump drive transmits torque to the “pump stack,” which includes the pressure-compensated pump for the motor and the clamp pump. The reservoir stores and cools the oil between cycles in the hydraulic system.

Older hydraulic systems used several types of transmissions between engine and pumps, including power-take-off (PTO) drives.  Vulcan used a direct drive which was basically a thin circular plate which transmitted torque from the engine to the pump shaft.  This seriously reduced mechanical inefficiencies in the system.

4200_1&2_Page_40
The hydraulic schematic of the system. Most of the fluid is stored in the reservoir (1) until drawn into the main pump (6) or the clamp pump (6e). The fluid driving the motors runs through the supply quick disconnects (12) to the hammer, and returns through the return quick disconnects (13). The oil then goes through the oil cooler (15) before returning to the reservoir (1). The clamp pressure, alternating between the two hoses (10) and (10a), is controlled by a directional control valve (7). The case drain line (19) goes directly to the reservoir (1) to minimise back pressure.

We can thus see the essential components of the hydraulic system:

  1. Prime mover (4).
  2. Pump to pressurise the oil (6,7)
  3. Equipment to do the work and depressurise the soil (motors, clamp)
  4. Cooling and oil storage (1,15) after oil is returned to the power system.

Pressure in Hydraulic Systems

Fluid power systems are designed to deliver an oil flow at a given flow rate.  So what pressure does this come at?  This is a key point in fluid power systems: pressure is determined, without any other restrictions, by the load itself.  This is true whether the load is rotational or translational, and in this system we have both.

Rotational (Motor) Loads

The main pump (6) is configured to, at maximum displacement, deliver a given flow of oil.  This in turn determines the rotational speed of the motor.  The power put into the system–a product of the pressure and the flow–varies with the load of the system, and that in turn varies with the pressure.  So are there limits to that pressure?

The answer is obviously yes.  Hydraulic systems, broadly, divide themselves into two pressure ranges: high and low.  Low pressure systems generally have their pressure limited to about 2500-3000 psi, and a wide range of hydraulic systems operate in this range.  High pressure systems run around 5000 psi and beyond.  Each system has its own standard of components.  The Foster 4200, in common with Vulcan’s 2300 and 4600 vibratory drivers, was a high pressure unit.

So how do we limit the pressure?  In “classic” systems such as the HPSI power packs Vulcan started with, there was a fixed displacement pump and a relief valve (11).  When the pressure reached the system maximum, the hammer would slow down and the excess oil would “dump over relief.”  This worked, but it generates a lot of heat, which means that the system’s thermal protection shuts it down in short order.

On this hammer, Vulcan used a pressure-compensated, “load-sense” system, which required a special relief valve which, in turn, informed the pump that maximum pressure had been achieved.  The pump would reduce its displacement as described earlier until the flow and pressure were balanced.  There was still a relief “just in case” for safety purposes, but much of the dumping over relief was eliminated.  This also enabled the operator to slow the hammer down without slowing the engine down, allowing the engine to operate in its best torque range.

Translational (Cylinder/Clamp) Loads

Before we describe the hydraulics, let’s look at what the clamp does.  Some types of hydraulic clamps are shown below (from this article.)

Figure54
Figure 54. Types of clamps that grip the pile using friction. a) clamp for steel pipe and reinforced concrete shells, b) direct-action clamp using a hydraulic cylinder and accumulator for sheeting and similar piles; c) lever-type clamp for piles and pipes.

Fun fact: Foster started this project using the clamp type (c), which they inherited from the Japanese.  This clamp was common when cylinders were not large and the lever action was needed to obtain the force, but these clamps were heavy.  Vulcan convinced them to convert to type (b), albeit without the accumulator, which had been a U.S. industry standard for a long time.  Vulcan also convinced Foster to adapt an integral clamp cylinder as opposed to the bolt-on types which are still common on American vibratory equipment.

The clamp is simple: the clamp in pressure is applied to the large (head) end of the clamp and the jaws close on the pile, clamping the pile and stopping the cylinder.  When driving is finished, pressure is applied to the small (rod) end of the clamp and the jaws open.  The speed of the movement either way is computed as follows:

V = \frac{231 \times GPM}{A}

where V is the velocity of the clamp in in/min and A is the area (head or rod) under pressure, sq.in.  Moving cylinders is a common hydraulic operation, one (with the right control system) can be done with great precision.  In this case positional precision wasn’t a big deal; the clamp cylinder just needs to go until the pile stops it.

So what happens then?  The system “deadheads,” and, with a fixed displacement pump, most everything goes over relief, with the usual heating problems.  There are ways of getting around that but here again pressure-compensated pumps are the best answer, going to nearly zero flow when the clamp deadheads.

Another fun fact: In adopting Vulcan’s clamp design, Foster also incorporated Vulcan’s safety check valve in the clamp, which continued pressurisation in the event the clamp hose was cut.  Foster also incorporated Vulcan’s interlock that made it impossible to start the hammer until the exciter was clamped to the pile.  That’s one reason why a separate hydraulic system is needed for the clamp; another is that full clamp force and pressure is guaranteed, whereas with the pump for the motor the pressure varies.

Conclusion

We’ve covered a lot of ground here.  Hopefully you’ve gotten a better idea of what hydraulic systems in general–using a real-life application–are all about.  Vulcan’s effort with Foster’s vibratory hammers was a unique one, and probably resulted in the best vibratory driver (if not the most economical to produce) Vulcan ever made.

Piston-Hydraulic-Pumps

Russian Hydraulic Demolition Hammers

Yu. V. Dmitrevich, VNIIstroidormash
L.V. Erofeev, Stroifundamentservice
V.A. Nifontov, Stroifundamentservice
D.C. Warrington, Vulcan Iron Works Inc.

This article was originally published in 1993 or 1994.  The graphic above shows a 9 kJ unit mounted on an excavator.

Introduction

Hydraulic demolition hammers mounted on hydraulically powered excavators are becoming increasingly widespread in world practice. They allow the excavators to be used for breaking rock and permafrost, break up large rocks, old foundations and reinforced concrete structures, and other jobs.

Outline of the Machine

Hydraulic demolition hammers are often equipped with hydraulic accumulators in the pressure line and sometimes in the drain line as well (as is the case with the Raymond hydraulic pile driving hammers) to achieve higher efficiency and to smooth pulses of fluid pressure in the hydraulics. Compressed nitrogen is mostly use as the elastic element in these accumulators.

The proposed hydraulic hammers differ from similar machines of leading companies outside of Russia such as Krupp of Germany, Montaber of France, and NTK in Japan. The main difference is in the accumulators the Russian machines have no compressed nitrogen accumulators, but are equipped with hydraulic accumulators having a so-called “liquid spring,” which is a closed volume of hydraulic oil compressed under pressure four or five times the pressure in the hydraulic system. Possible leaks from the inside of the hydraulic spring are compensated automatically when the hammer is switched off. Such a hydraulic accumulator does not need any adjustments and control during operation and its parts can serve as long as the hammer itself.

The main reason this design was chosen relates to the conditions in Russia itself. The temperature gets very cold, down to -60° C under these conditions the rubber in the bladder type gas accumulators will become embrittled in the temperatures common in many parts of Russia. Once this has happened, the bladders will burst and the machine will have to be completely disassembled and the bladder replaced. This operation is tedious enough on a normal construction site it is a greater problem when the job is somewhere above the Arctic Circle in Siberia.

Another specific feature of these hydraulic hammers is that their rams are not integral with the piston but are connected with the latter through a special elastic hinge. All the hydraulics of the hammer are centralized into a separate unit comprising the working cylinder, distribution valve and hydraulic accumulator. The ram can be of any size as required. The weight of the ram is selected so as to provide the impact energy at an impact velocity of no more than 6 m/sec. The weight of the ram is generally double that the the impact tool with other machines, it can be only half. This provides a high impact efficiency and increases the efficiency of the hydraulic hammer as a whole.

The power output of an impact hammer is the product of the impact energy of the hammer and the number of blows per minute. Thus, for the same power output an impact hammer can have either a high number of blows per minute and a low rated striking energy or a low number of blows per minute and a high impact energy. The advantage of the latter condition, however, is that the higher impact energy can be decisive in producing the high impact force levels necessary to demolish the work at hand. This is why these units have demonstrated outputs two or three times as high as those produce by Kone (Finland,), Krupp (Germany,) and have also outperformed those from Ingersoll-Rand.

The efficiency of these hammers is further promoted in breaking permafrost and rocks by the streamlined shape of the tool itself, which permits the operator to sink the whole hammer into the medium to a greater depth than just the length of the impact tool, i.e. a deeper layer than can be broken at one pass. Thus, there is no need to make the tool very long and the hammer can be operated as a lever, tearing large pieces away from the permafrost or rock. Other companies prohibit such handling of their demolition hammers. The strength of the tool and of the hammer body permit such operation in the case of the Russian machines.

Table 1 shows the standard sizes of the hydraulic demolition hammers based on these principles.

Table 1 Specifications for Hydraulic Demolition Hammers

Specification

Size I

Size II

Size III

Size IV

Size V

Impact Energy, kJ

1.8

3

6

9

20

Blows per Minute

300

180

240

160

125

Hammer Weight, kg.

450

840

1500

2100

3700

Ram Weight, kg.

100

200

400

600

1000

Weight of Impact Tool, kg

50

100

200

300

Insertion Diameter for Impact Tool, mm

100

135

150

180

Hydraulic Oil Consumption, l/min

120

120

165

165

200

Working Pressure, MPa

16

16

16

16

20

Connecting Hose Size, mm

20

20

25

25

Weight of base excavator, metric tons

6-12

10-20

18-25

20-36

30-45

Maximum depth of loosening of permafrost or rock per pass, mm

600

800

1000

1200

The Size I has been produced in Belarus since 1982 and the Size IV in Russia since 1978. Sizes II and III have been tested as prototypes and are proving to be the most popular sizes. The design of the hammer is patented in Germany, Hungary and Finland.

Hydraulic hammers of Sizes IV and V may be used for driving small piles after some modification.

Description of Design

The hydraulic demolition hammer is mounted onto excavators as an interchangeable tool by means of an intermediate bracket which is secured both to the excavator and to the hydraulic hammer

Figure 1 shows the main parts which constitute the structure of the demolition hammer. The working cylinder (Figure 2) is essentially a body having a heat treated steel sleeve inserted therein, the latter accommodating a piston moving therein. The body of the work cylinder accommodates a check valve and a hydraulic accumulator comprising a piston with a head and rod, a bushing and a fluid spring enclosed in the cavities bored into the body and communicated with each other and with the rod end of the accumulator by means of ports.

As shown in Figure 3, a plug is provided to let air out from the cavity of the fluid spring when the latter is being filled with the working fluid.

HYDFIG3
Figure 3 Plug for Air Outlet from Fluid Spring 1) Working Cylinder Casing 2) Plug 3) Sealing Ring 4) Air Outlet Plug 5) Fluid Spring Cavity

The rod of the hydraulic accumulator is spring loaded. The head end of the accumulator is communicated with the fluid spring through a check valve intended to compensate for leaks from the cavities of the fluid spring when the hydraulic hammer is switched one and off. The work cylinder is closed from the top with a lid.

The impact portion of the hydraulic hammer is suspended from the rod of a piston by means of rubber shock absorbers. These decrease the dynamic loads acting on the rod. The impact portion moves in the guide pipe. Ports are provided in the upper and lower portions of the guide pipe and these intercommunicated by air ducts. With the impact portion moving, air flows freely from one cavity into the other one through the air ducts.

The impact portion delivers by its lower end blows upon the tool, which can move freely downwards for 60 mm along the guide of the axle box mounted on the guide pipe.

Principle of Operation

Looking at Figure 4, the ram, rod and piston are in their initial position, which is resting on the impact tool. The control valve occupies the upper position under the action of a spring mounted under its lower end position. This communicates the rod end of the work cylinder with the pressure line. It also communicates the head end with the drain line of the hydraulic system, the piston of the hydraulic accumulator occupying the upper position.

After the pump is started, the working fluid gets through the valve into the rod end of the working cylinder and the space above the piston of the hydraulic accumulator. As a result of this the impact portion starts accelerating upwards. This forces the fluid from the head end of the working cylinder through the port along the drain line into the tank, whereas the piston of the hydraulic accumulator moves downwards.

Moving on to Figure 5, at the end of the upward acceleration, the piston passes the drain port, as a result of which pressure in the head end of the working cylinder, the duct and above the upper end of the valve rises. Since the area of the upper end of the valve is greater than that of the lower one, the valve moves into the lower position, thereby communicating the head end with the pressure line and the rod end with the drain line.

This is followed by the phase of slowing the ram to a stop in the upstroke, whereby the piston forces the fluid from the head end into the hydraulic accumulator.

After the ram has stopped at the top of the stroke, it starts accelerating downward under both the force of gravity and the fluid pressure on the head end of the piston. After the impact portion has acquired a speed where it outruns the hydraulic pump, the hydraulic accumulator starts to discharge, and its piston moves upwards. At the end of the downward stroke the ram strikes the impact tool, which moves relative to the body of the hammer so the tool can penetrate the soil. Before the blow is delivered, the upper edge of the piston lowers below the check valve, whereby the head end is communicated with the drain line. As a result of this, the pressure in the head end and above the upper edge of the control valve drops down to a value at which point the spring mounted under the control valve can move the control valve upwards.

After this, the cycle can be repeated. Figure 6 shows the hydraulic schematic for the system.

HYDFIG6
Figure 6 Hydraulic Schematic of Demolition Hammer 1) Check Valve 2) Working Cylinder 3) Control Valve 4) Check Valve 5) Fluid Spring

Additional Features

The fluid spring is used in the structure of the accumulator. In this spring the pressure exceeds that in the hydraulic system by as many times as the area of the piston exceeds the area of the rod entering the cavity of the fluid spring.

Possible leaks from the cavity are compensated by the hydraulic system after the pump through the check valve, with the piston being displaced by the spring mounted thereunder.

The hydraulic hammer cannot be started unless it is applied against the work. Without the work being applied against the impact tool, the block head occupies the lowest position and the upper surface of the piston is lowered below the ports through which the fluid gets into the rod end. An attempt to start up the hammer without the hammer applied against the work results in the fluid passing freely over into the tank, and the hammer does not operate.

Conclusion

The hydraulic demolition hammer with fluid accumulator has proven itself both in theory and in practice. It has as rugged and simple design and is capable of performing many kinds of work. It overcomes many of the difficulties of other designs without unacceptable compromises in performance.