Decelflo Pile Hammer Muffer, and the Thruflo Muffler

One thing most people notice first about pile driving jobs is that they generate an elevated level of noise. Until the 1960’s, most people simply put up with this and many other aspects of industrialisation and development. In the early 1970’s, Vulcan and other pile driving equipment manufacturers were confronted with new regulations–both at the federal and local level–which sought to regulate the noise output of construction equipment. Needless to say, pile driving equipment was high on the list.

Vulcan’s first reaction was to study the issue. It retained the services of United Acoustical Consultants in Glastonbury, CT, and its principal, Stannard Potter, to study the nature of noise output of Vulcan hammers. In December 1972 they conducted a study of a Vulcan #1 at the Chattanooga facility, and the report on the test is shown here.

Vulcan hammers, although durable and simple, suffered from two specific difficulties for noise abatement: a) their open construction gave little natural noise attentuation, and b) their lack of a recoil dampener increased the impact load on the frame, thus making it difficult to attach shrouds and other devices to attenuate sound. However, one of the results of the study was that a large proportion of the sound emission from an operating Vulcan hammer came from the exhaust. Since muffling the exhaust was simpler than doing same with the impact, Vulcan commissioned Potter to design an exhaust muffler, which it called the Decelfo Muffler.

Below: a diagram of the Decelflo Muffer concept, from Potter’s U.S. Patent 3,981,378.


Setting up for the test. The muffler (the silver device at the top of the photo) is mounted on the hammer through the sheave pin, which principally is the centre shaft for the sheave wheels used to raise and lower the hammers. The bearings for the sheave pin on the muffler were connected to the muffer through rubber shock absorbers. The hammer’s exhaust was connected to the muffler using hose. In front of the hammer Stan Potter (right) reviews the test procedure. At the left is Henry G. Warrington, Chairman of the Board and President.

The muffer was simple, a box which directed the air or steam output of the exhaust through perforated pipe surrounded by acoustical foam. The drawing shows a stacked arrangement for the muffler, but Vulcan never employed this arrangement.

The first test of the Decelflo took place in October 1973 in the Alameda yard of Santa Fe construction in Alameda, California. It involved muffling a Vulcan 020 hammer.

As shown below, the test was successful; the muffer performed as anticipated and its used resulted in reduction of hammer noise.


Flush with this success, Vulcan continued in its development of the muffler. In July 1974 it had another opportunity to demonstrate (and verify) the Decelflo’s capabilities, this time in Chicago at a sheet piling project. Below: the Decelflo mounted on top of the Vulcan hammer, in this case a 50C. The hose connection from the exhaust port to the muffler can be clearly seen, along with its connection to the hammer via the sheave pin. For a photo of the muffler in action during pile driving, click here.

Decelflo Muffler in Chicago before its test.
Recording of the results of the test, 31 July 1974

Vulcan had great plans for the Decelflo; at this time it was working on a method to mount the muffler directly on the hammer, as shown below.


But then things took a strange twist.

To begin with, there was considerable contractor resistance to the concept of having to add another device to the hammer assembly. Mounting it above the hammer lengthened the leaders required to operate the hammer, and the large installed base of Vulcan hammers dictated that this would be the normal way the muffler would be mounted.

Beyond that, the level of noise emissions, and how people perceive them, vary widely from one jobsite to another. This variation is a function of the location of the job (urban, remote, etc.), the presence or absence of neighbouring buildings to reflect the sound, and whatever ambient noise is in proximity to the jobsite. For example, driving piling next to an existing interstate, with the road noise already present, may not be very perceptible.

Finally, as far as those working on the jobsite are concerned, contractors (and OSHA) found it simpler to deal with noise emissions from pile drivers and other equipment on site by providing hearing protection to the workers, which of course is standard on jobsites today.

In any case, the Decelflo muffler was never very popular, “noise pollution” never achieved the notoriety of air and water pollution, and both Vulcan and its customer base moved on to other concerns. For his part Stan Potter moved on to patent the Decelflo concept independently of Vulcan.

Thruflo (Geothermal) Muffer

The need to attenuate noise combined with another concern of the era, the need for alternative energy resources, with the geothermal muffer. An experimental product, it nevertheless touched on issues that are still important today.

Geothermal energy is possible when the hot magma which exists in the earth is close enough to the surface and the underground water to turn the latter into steam, which can be used to drive the turbines and generators to produce electric power. The means that the source of geothermal energy is not only free economically, but also that carbon dioxide (greenhouse gas) is not emitted in the production of electricity.

In the course of producing energy, the steam is vented to the atmosphere, and unmuffled this can produce a high noise level.

The target for the geothermal muffer: The Geysers, a power generation plant north of San Francisco, CA, in February 1974.

Vulcan built a prototype and tested it in its own facility in August 1974.

The Thruflo Geothermal Muffer, ready for acoustical testing. Above it is the straight pipe, against which it will be compared. Steam flowed from left to right.

A video wasn’t recorded, but this series of photos is shown with an audio recording of the test 1 August 1974.

Unfortunately the Thruflo Muffer did not get past the prototype shown above. Some of the mufflers that did make it to The Geysers had a difficult time of it, as this report attests.


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