Knockout Rings, Large and Small

Above is a chart from 1965 of knockout rings for Vulcan hammers from the #2 to the 020/200C series.  The knockout ring is, in some way, a short version of the capblock follower/shield for softer cushion materials.  It replaces the integral ring which has  been standard on Vulcan hammers.  (Some explanation of both is here.)  Vulcan’s literature from the 1970’s explained it in this way:

To facilitate the quick change of cushion material to eliminate down time on the pile rig the Knockout ring configuration was introduced.  It is common practice to have one or more extra Knockout Ring cushion receptacles on the job site to insure quick change and continuity of driving time.

As in the Integral Ring configuration, this type has the same vertical depth limitation by virtue of design…

With the Knockout Ring configuration used…it is necessary to use both a Top Plate and a Bottom Plate.  the Bottom Plate is required  to prevent the cushion material from extruding underneath the Knockout Ring laterally…

The arrangement Vulcan had in mind is shown below, again from a 1965 drawing.


The problem with the bottom plate was that it shortened the cushion stack.  When it is omitted, the problems Vulcan anticipated take place, and the knockout ring gets knocked out (by the ram point clipping the top of the ring.)  It’s also inadvisable to use one in a situation where there is a great deal of “bounce” (low impedance pile, high quake soil) in the hammer-pile-soil system.

Knockout Rings weren’t intended as a repair for damaged integral ring, but were sometimes used that way.

Vulcan’s Blow Count Specifications

The durability and longevity of Vulcan pile hammer is something that is seldom replicated in just about any other manufactured product.  Since pile driving is self-destructive on the equipment, this is a remarkable achievement, but it should be tempered by the fact that it’s possible to render a Vulcan hammer inoperable by the way it’s used.  There are many things that can make this happen–inadequate or nonexistent hammer cushion material or lubrication to mention two–but the one thing that Vulcan decided to include in its warranty was the blow count specification.

Recording the blow count–the number of hammer blows per inch, foot or metre of pile advance–is virtually universal on pile driving jobs.  The dynamic formulae basically translated blow count into pile capacity.  While anyone familiar with pile dynamics understands that blow count is a crude measure of the response of a pile to impact, including a blow count specification is a good first measure of both the advance of the hammer and also how much energy is being returned to the hammer, which is a case of hammer damage.

Blow count-resistance graph, developed by Vulcan in the early 1990’s as part of its effort to educate state and federal agencies on the basics of pile driving. As the blow count increases, the amount of SRD (soil resistance to driving) increases, but at a progressively slower rate. This indicates that simply increasing the blow count is a “diminishing returns” proposition, destructive for hammer and pile alike.

High blow counts indicate that more and more of the energy was going back into the hammer rather than into the pile, thus increasing the danger of hammer damage.  They also indicate that pile top stresses increase with higher blow counts, as the movement of the pile to mitigate the maximum impact force decreases.  Thus high blow counts just to get the pile to tip elevation without considering changes in hammer or basic drivability considerations is a losing proposition.

Starting in the late 1970’s, Vulcan voided the warranty on its hammers if the blow count exceeded 120 blows/foot.  It’s interesting to note that Vulcan never made its specification in blows/inch.  This was true for its onshore hammers; however, for its offshore hammers it was forced by circumstance to increase the hammer refusal criterion as follows:


Vulcan hammers are designed to withstand a continuous driving resistance of 120 blows/foot (400 blows/meter). In addition to this, Vulcan hammers will withstand refusal driving resistance of 300 blows/foot (1000 blows/meter) for five (5) consecutive feet (1500mm) of penetration. Any resistances experienced in excess of these are beyond rated capacity and will void the warranty. This definition is not an exclusive definition of excess of rated capacity and other criteria may apply.

1 Specification applies to all Vulcan offshore hammers, not just those listed in this catalog.

This was drawn from the API RP 2A specification, which was discussed relative to pile stick-up.  An elevated refusal blow count specification was justified by two things.  First, the offshore hammers were more robustly built than the Warrington-Vulcan hammers which made the company famous, as they were derived from the Super-Vulcan hammers.  Second, the remoteness of offshore job sites made high blow counts a necessity, as bringing a larger hammer to the job was frequently impractical.  (Improved methods of drivability predictability lessened the possibility of this happening.)

Blow count limiting warranty specifications are not an absolute method to prevent hammer abuse, but they’re a good start, and Vulcan used them to the advantage of itself, its end users and the owners of the projects where Vulcan hammers were used.

Driving Piles with Stub Leaders and a Template

The best known setup for pile driving equipment is a crane and a set of full-length (of the pile and hammer) leaders, attached to the crane in a variety of ways.  But another alternative is to use a “stub” leader, i.e., one that is very short, and a template to align, position and guide the pile.  This is traditionally associated with steel piling, so we’ll look at this first.

For these hammers the platform itself is the template, the piles are driven from the top through the legs.  Most conventional platforms had angled legs so the hammers almost invariably drove on a batter, which gave rise to the “stick-up” problem, more about that below.

But using stub leaders and a template isn’t restricted to steel piles; it has also been done on concrete piles, as can be seen below.

From a contractor’s standpoint, handing hammers in stub leaders requires a considerable level of skill from the crane operator, but the weight savings and ability to handle the hammer in difficult situations makes the use of stub leaders, when possible, a very attractive option.

Engineering Aspects of Stub Leaders

From the photos above, you can see that piles can be driven with stub leaders either plumb or on a batter.  Plumb piles are not much different with stub leaders than with conventional leaders: the key is to have the hammer straight and square on the pile, which means that the leader setup should be balanced to hang straight and side forces on the hammer be avoided.

With batter piles, since the offshore industry used them (and still does) intensively, the most complete specification for such piles is the American Petroleum Institute’s RP2A specification.  With stub leaders the pile basically supports the hammer during driving, and the hammer in turn loads the pile with both the impact loads and the static load of the hammer assembly, which in turn acts both parallel and perpendicular to the axis of the pile.  Basically there are two important engineering aspects to configuring driving batter piles with stub leaders on a template:

  1. Column buckling due to the weight of the hammer acting on the axis of the pile.
  2. Beam loading of the hammer due to the component of the weight which acts perpendicular to the axis of the pile.  This creates a cantilever beam with a maximum bending moment at the template.  Obviously the weight of the hammer assembly (along with the weight of the pile) will induce bending stresses.  These stresses are both tensile and compressive, and both are important to the structural integrity of the pile during driving.  The template must also be designed to handle the loads and moments on its structure.

With steel piling, the combined weights of hammer assembly and pile limit the permissible length of the “stick-up” of the pile.  Steel piles are easily spliced and added on to, so piles which are much longer than the stick-up can be drive.  (Piles which are much longer than practical lengths of conventional leaders can be driven as well.)  With concrete piles, these can be splices but there is less flexibility and less resistance to bending moment with splices, which limit the possibilities of driving these with stub leads on a batter.  (The ability or lack thereof of concrete to withstand bending stresses also complicates the situation.)

One more important point: the weight of the hammer assembly cannot generally be assumed to be at the pile head, but above it.  That’s why the center of gravity information is so important for offshore driving, which led to Vulcan tips such as this.

Stub leaders combined with templates is an attractive option for driving piles, but proper engineering and construction procedures must be followed for successful results.


Vulcan’s Most Famous Sheet Piling/Extractor Photo

The photo above, dating from 1949, shows a worker tightening the bolts on the connecting links of a Vulcan extractor to the top of a prepared sheet piling in preparation to impact the sheeting upwards and take it out.  This photo was used for many years in Vulcan literature, including Vulcan Bulletin 71B.  (Note: don’t try this now without a safety belt and other safety equipment for the worker!)

The project it was on was in familiar country to Vulcan: it was for the Calcasieu River Bridge between Westlake and Lake Charles, LA.  The owner was the State of Louisiana Department of Highways.  The contractors were Kansas City Bridge and Massman Construction, still a user of Vulcan and Conmaco equipment.

It’s also interesting because it’s similar to the “sheet pile setter” logo that Pile Buck has used for many years in its own logo and advertising.

Parts Diagram for DGH-900 Hammer

Above is a parts diagram for the Vulcan DGH-900 hammer, from the late 1950’s.  It’s similar to the DGH-100 hammer.  More information about these hammers is here.  The complete Field Service Manual for both DGH series hammers is in the Guide to Pile Driving Equipment.

An Overview of Tapered Pipe Threads, and Their Application at Vulcan

It’s hard to imagine that much of our technology is underpinned by very old, basic standards that year after year simply “do their job” without much regard.  One of those is tapered pipe threads.  This is a brief overview of same, and specifically the “National Pipe Taper” or NPT threads.  Much of this material comes from the American Machinists’ Handbook by Fred Colvin and Frank Stanley, Second Edition (1914).

Most screw threads are “straight threads,” i.e., the diameters of the threads (outside, pitch, inside) are constant along the length of the threads.  Tapered threads by definition can only work for a limited length, but when pipes are connected, that’s fine.  Like any other taper lock, tapered threads have an additional wedge effect, which means that they can seal fluids in the pipe (or outside of it.)

Originally these pipe threads were referred to as “Briggs standard threads” after Robert Briggs who came up with them.  In 1886 these were adopted as a standard by the American Society of Mechanical Engineers and various manufacturers.  They have varied little since that time.  They have been a durable standard for leak-resistant, permanent (and semi-permanent) connections ever since.

An overview of the “Briggs standard thread” is below.


As noted above, only the “perfect” threads (in one way or another) contribute to the sealing/joining of the pipe thread.

The overall dimensions of the various sizes of tapered pipe threads are shown below, with a diagram showing the types of gauges used to check the threads.


The tapered reamer was one item Vulcan seldom used; the usual procedure was to tap drill the hole and then use a tap for the threads in question to put the threads in the hole.  Below are some tap sizes for NPT (National Pipe Taper, or Briggs) threads.

Tap drills for National Pipe Taper threads.  The “Briggs” values are for the NPT threads; the Whitworth are for their UK counterpart, which were never as popular as the NPT/Briggs threads.  The drill size for the 2″ pipe tap should read 2 3/16″.  In reality there is a little “wiggle room” for the tap drill size, as is the case with straight threads.
When threading a pipe, a die is generally used. The “actual inside diameter” can vary; the table here is closely related to Schedule 40 pipe. It can obviously be smaller for higher pressure applications and those where the mechanical strength of the connection needs to be larger (as with pressure gauges.)

A more detailed treatment of the threads as the pipe and hole threads interface is shown below.

Theoretical standards for the NPT/Briggs standard pipe threads, with a more complete treatment of the perfect and imperfect threads, which is important in the design of pipe threaded holes, specifically how deep they need to be.  This comes from “The Crane World” magazine, January 1919, from the Crane Company, a leading manufacturer of valves.  When the Crane Company was established in 1855, it was near Vulcan’s facility and in fact Vulcan’s founder, Henry Warrington, was Crane’s first customer, placing an order for box castings (a notoriously difficult shape to cast) and other parts for locomotives, which Warrington was making at the Vulcan Foundry.  In his later years, after his sons were active at Vulcan and their other activities, Warrington worked at the Crane Company.

The pipe taper standard was wildly successful, and is used in everything from home plumbing to high-pressure hydraulics.  In the oilfield the standard was so successful that it’s widely used even in places where metric standards are the norm

As far as Vulcan is concerned, Vulcan used the standard in many of its products, both the air/steam hammers and later the hydraulic vibratory hammers, where they were used for pressures up to 5000 psi.  This was due to their durability, ability to resist vibration (a must with any Vulcan product) and their flexibility in radial orientation.  With a pipe thread there is a point where it’s “tight” but it can generally be tightened a little further, thus allowing some flexibility in the orientation of parts.  One thing Vulcan learned with pipe threads was, although they are designed to seal with their taper, the use of some kind of “pipe dope” or sealant is very important.

Below are some applications of pipe threads in Vulcan hammers.

A Vulcan drawing “callout” for pipe threads, in this case small ones for the grease fittings on the Hydra-Nut.
The “outside” of the Hydra-Nut (U.S. Patent 3,938,427.) Introduced in the 1970’s to directly replace the cable nuts (as shown above,) the Hydra-Nut simplified the process of tensioning the cables. The Hydra-Nut was screwed on without the cast thread protector cap on the top, the cable was lightly tensioned with a “manual jack,” the threaded sleeve was screwed down on the cable fitting and tightened against the jack body, the manual jack removed and thread protector cap replaced (aligning the flats on the cable fitting with those on the cap,) then the chamber was pressurised through the grease fittings to the pressure where the cables would have their proper, full tension. The weakness of the Hydra-Nut was in the grease fittings; should dirt or paint get in them, the chamber would depressurise and the cables would be loose. This was more probable when Zerck fittings were used than with the button head fittings as shown. Vulcan addressed this issue in the 1980’s with the Auto-Jack, which altered the Hydra-Nut by adding an internal cable nut with the integral jacking cylinder, which was then depressurised when the cable achieved proper tension.
A call out for a pipe flange on a Vulcan offshore hammer. Note that now, instead of tap “drilling,” we’re forced to bore the hole before putting the pipe tap in.
A close-up of the 040 cylinder during exhaust. The large hose is the steam hose that powers the hammer, the small hoses are the Vari-Cycle hoses that shift the trip shifter one way or the other to vary the stroke. The hose is connected to the hammer through a connector which is screwed in the large pipe caps on the double pipe flange in the front of the hammer.
Vulcan 85C Hammer.  Note that, towards the top of the cylinder are two pipe plugs.  These are installed into tapped tapered pipe fitting holes.  (There are actually four of these, two are covered by the plate referred to as a “belly band.”)  Behind them is a cored passageway between the valve and the top of the cylinder.  These holes helped to support this core during casting but had to be plugged for use, and the pipe plugs were the ideal way of doing this.

Pile Buck Ads 5: Vulcan 530 in Offshore Leaders —

For the last of the “Pile Buck Ads,” a photo of the Vulcan 530 hammer is featured in offshore stub-type leaders. The 530, introduced in 1978 for driving pipe piles offshore in the Gulf of Mexico, was and is used in a wide variety of pile driving projects. In this case it’s shown to be […]

via Pile Buck Ads 5: Vulcan 530 in Offshore Leaders —

Hong Kong and the Straits of Hormuz: It’s Amazing It Took This Long

Although Vulcan exported its pile driving equipment from the start, it was it’s foray into the offshore oil business that gave Vulcan a truly international perspective.  That perspective put some of the world’s “hot spots” into its field of interest, and two of them are very active these days: Hong Kong and the Straits of Hormuz.

Most of Vulcan’s activity in East Asia was in South East Asia; thus, its main “centre of focus” for its equipment and travelling personnel was Singapore.  With Vulcan’s sale of its first pile hammer package to the Petroleum Corporation of the People’s Republic of China in 1981, Hong Kong became of interest.  At the time China was a very closed country; Hong Kong acted as a window to the world, although from a commercial standpoint Vulcan didn’t use it that way.

The UK’s decision to return the entire colony to the People’s Republic when the lease on the “New Territories” (the area of Hong Kong north of Kowloon and excluding that and Hong Kong Island) expired in 1997 was formalised in 1984; however, rumours swirled about a handover years before.  The attitude of Vulcan’s business associates towards such a reintegration was bluntly summarised by one of them: “They’ll screw it up.”  The contrast between the state socialism of the People’s Republic and the free-wheeling capitalism of Hong Kong was pretty stark, and it was hard to imagine that the former would allow the latter to go on in the same way for any length of time.

Up to now the PRC has surprised many people with the relatively light hand they’ve actually had on Hong Kong.  Some of that was the desire of the PRC to have Hong Kong be a “model province” for the “capitalist roaders” in the rest of the country, an incentive for economic development.  Another factor was to make the reintegration of the greatest “wayward” region–Taiwan–more attractive to those on the island.  Still another was the PRC’s desire to maintain Hong Kong as an economic powerhouse and thus contribute to the country’s overall prosperity.

Such desires have butted up against two things: the linking of Hong Kong’s people of free expression to economic freedom, something the mainland has avoided, and recent changes in the Chinese leadership.  Now the latent conflict of the two is out in the open.  The Chinese leadership will have to tread carefully; if they don’t, they could fulfil my business associate’s prophecy and China will be the worse for it.

The Straits of Hormuz has been the central “choke point” of world oil shipments for many years.  The Persian Gulf is ringed by oil-rich nations and 20% of the world’s oil supply passes through it.  That vulnerability really came into public consciousness with the Yom Kippur War and the first “oil crisis” of 1973.  It wouldn’t take much to mine or otherwise sabotage the Straits of Hormuz, which increased the Western military interest in the place.

The countries that ring the Gulf have been aware of this vulnerability for a long time.  Saudi Arabia built its Yanbu oil terminal on the Red Sea in an attempt to provide an alternative to the Straits.  Vulcan’s first contact with and sale to the Korean contractor Hyundai was due to the fact that they were contracted to build this terminal and need pile driving equipment to accomplish it.  On the other side Iran was looking to build a major port at Chabahar on the Indian Ocean using Vulcan’s long-time customer Brown and Root, but the 1979 Revolution stopped that effort.  (The Islamic Republic built a port there, currently operated by India.)

With the Sunni-Shia divide and the ill-conceived war in Iraq (which deprived the two sides of a buffer) the Straits had opponents on both sides, and it was only a matter of time before it would become a hot spot once again.

The amazing thing in both these situations is not that they’re points of conflict, the amazing thing is that it has taken as long as it has to reach the current situation.

Pile Buck Ads 4: Link Belt Diesel with a Mandrel —

The fourth in our series on the ads which Pile Buck allowed to run was this shot of a Link Belt 520 driving shell piles using the Vulcan Expanding Mandrel. The mandrel’s history and shell piles in general are discussed here. The Link Belt 520 is an interesting story in itself. The diesel […]

via Pile Buck Ads 4: Link Belt Diesel with a Mandrel —