EVOLUTION, ACCUMULATOR TO PRESSURE PULSATION DAMPER
aka PUMP PULSATION DAMPER
In the 19th century, fire engine pumps used an air bottle to smooth the flow.
This was shown in the 1900s 4th grade school physics text books, and used
to demonstrate a use for Boyles law of gas compression and expansion.
In world war II a Mr Mercier colaborated with a coleague Edward Greer, also
a draftsman at Stein Atkinson company USA, to produce a bladder accumulator.
The principal was that a cylinder will expand first from its largest daimeter.
If the cylinder also has an increasing wall thickness progressivenly from
largest diameter to smallest diameter it will follow the law of progressive
expansion, aka derived from "hoop stress" t=P.Ri/Se-0,6PThereby “sweeping”
out of the way, liquid between the elastic wall and the outer metal housing .
Making the expansin of th bladder perfom like a piston.
The Mercier Greer project was supported by the dept of the US NAVEY.
THE “BLADDER” (gas bag) ACCUMULATOR
The purpose of the "bladder" OR GAS BAG was to enable air or gas to be
contained at or near a proposed pumping system pressure, thereby reducing
the volume necessary which would otherwise have to be compressed up from
The bladders of the Mercier-Greer accumulators were constructed from multiple
elastomeric moldings clued or "bonded" together, and the "bladders" were
prevented from escaping into the liquid flow by a "poppet" valve - being a diesel
engine exhaust valve, spring loaded in the open "off seat" position.
The Mercier Greer accumulator was licensed around the word by OUEAR France
and Greer Hydraulics inc., who had moved to California to escape East coast labor
In the 1965 Rod Fole, an engineer at Fawcett Preston and Company, who
had become a Mercier Greer licensee, showed a small bladder that was molded
as one piece without glue or bonds. Fawcet also dispensed with the anti extrusion
poppet valve, but GLUED a metal pellet on the liquid exhaust end of their elastic
gas containment "cup" shape. This was for use in a 2000 psi hydraulic cushion
for fork lift trucks.ka known as a "HYDRACUSHION"
The Fawcett Preston Ltd company was down sized, Fole left, but the Mercier
Greer fluid power oil Accumulator, predominantly 3000psi and 5000psi,
business remained with the down sized company.
As a remaining sales engineer the task was to expand the "hydraulic oil fluid
power accumulator business". There was obviously a potentially large market
for hydraulic flow and pressure smoothing versions of accumulators.
These days often referred to as "pump pulsation dampers".
It was apparent to me that the use of low grade elastomer gas bags, generally
cured or "cross linked" with sulfur, that enabled them to be glueable or
"bondable" after molding , was not good for pulsation damping at high or low
temperature, nor for a wide range of synthetic hydraulic fluids nor chemical
processes and other common liquids, other than mineral hydraulic oil .
This was because the more agressive liquid would attack the glue.
Further more the poppet valve arrangement restricted flow and reflected
pressure waves. The basic idea of having gas in a bag, and liquid in the
pressure carbon vanadium steel shell restricted use to non corrosive
Fawcett showed no interest in product development , so upon having my
employment contract varied by a reduction in pay from 1% to 0.1% i left
Fawcets and purchase "Compact Hydraulica Ltd" from George Moxson
Mining, and started to think about overcoming all the negatives of their
Mercier Greer design, applicable to pump pulsation damper applications.
As I had a personal notebook full of fluid power industry “complaints” ;
why will the Mercier Greer design not do this - do that etc; my first effort
was to address these "hydraulics" issues.
1. Any membrane should be molded from the least reactive formulation of
any given type of elastomer.
2. Prevention method of membrane extrusion into the system, forced by the
pre-fill (aka “pre-charge”) gas cushion pressure, should NOT reflect pressure
3. Instantaneous response to the need for high flow rates should be provided.
The answer for the 1000psi through 6000psi fluid power market, was what
became accepted as the PISTOFRAM. See examples USA Patent 3, 537, 357
Germany Pat 1775721
PISTOFRAM UK Patent 1183477 Sept 1967
Being a combination of a piston and the phoenetic for diaphragm, "fram".
The hesitation - “stick slip” or break out stiction mementary delay of piston
seals, was accommodated by minimal reaction time of a small mass
The time in which the piston began to move was acceptable because
diaphragm deflection was providing volume displacement, for that instant.
To ensure response the typical accumulator single connection was deleted,
and replaced with an inlet and an outlet, both being off center.
The off center porting arrangement not only caused pump pressure pulsations
to pass into the damping chamber instead of “bypassing” in a T connection ,
but also made it possible for a single hole into a piston containing a
diaphragm , which could never align itself with a place through which to extrude.
This was because when the piston reached end of stroke - in either direction
- which is when a pressure differential could be experienced, the port into
the diaphragm chamber of the piston was sitting flat against the end closure .
The multi-port through-flow configuration was called pulse “interception”.
and served us well. See examples US Patent 3,537,357
There was an additional design benefit. When causing a stream of high
frequency pulses to enter a chamber of much larger diameter than the entry
point, the amplitude of the pressure peaks is decreased because of the
distance to the nearest point of a reflection surface .
Not only was the small mass of the diaphragm essential to its design
responsive capability but also the difficulty of molding special formulations
of elastomer, and tooling costs, were greatly reduced compared with gas bag
“bladder” moldings. My company “HydroTrolE” Ltd. had its first fluid power
product range of sizes for high pressure hydraulics pump pulsation dampers
and “noise” reduction units that also accumulated volume.
Development ensued, in which dynamic sealing of the piston was greatly
improved. At that time the norm for piston accumulators was to place the
seals at either end of the piston “skirt”. This arrangement was said to be so
that the seals would act as bearing to prevent piston “wobble”. However
with seals wide apart, the annular volume between them, allowed seals to
deflect until pressure equilibrium was reached between the system and the
annular volume. This unavoidable seal deflection increased stiction against
the honed bore. We placed the seal close together and provided graphite
filled PTFE bearings at piston ends.
To make it possible for the dynamic seal to have reduced hysteresis,
I reduced the necessity for them also to provide static sealing when under
differential pressure at end of stroke. A face seal was installed on the end
plugs, now when shut down the dynamic seals experienced no differential
pressure . Seal compression was reduced to half the seal manufacturers
norm, reducing wear and breakout stiction .
Diaphragm life has certainly reached near 50 years and seal replacement
more than a decade in a well filtered systems. UK and German patents
were also granted.
A SUBSIDIARY MATTER
Other piston type products were added using the same modular
components - but not the hollow piston. These included proximity switch
stored volume indication units known as my MAGDACC range. The piston
accumulator market expanded in the ‘70s because when a piston
accumulator fails, it is not a suden failure similar to an elastomeric
membrane rupture, making piston accumulators a preference in the North
Sea hydrocarbons production platform, stand by power for valve actuators
etc, market which was opening up at that time.
BACK TO DAMPER APPLICATIONS
From the starting point of thousands of psi pressures, we began to create
a pulsation interceptor more suited to fluids other than those used in
The parameter aims were :-
1. To equal or exceed the 200 Hz. response characteristics of the
“PISTOFRAM” described above. This being necessary for addressing the
millisecond velocity jump shock generated by pumps running at less than
typically 95% volumetric efficiency.
2. To obviate any need for the pressure shell of the damper to be made
from high cost corrosion resistant materials.
3. Use the better formulations of elastomers similar to the elongation at break
softness and tensile strengths initially developed for the piston diaphragms.
An idea, later known as the HYDROCRAT, had the focus of my attention .
When a deformable cylinder of constant wall thickness , and one closed
end, is caused to collapse , it will do so in the form of a three pointed
“star”, but if one wishes to impart stability then cause it to collapse into a
cruciform cross section, and it will remain even more stable by “cork-
screwing” and reducing in length . (see for example US Patent 348393)
by the Hydrotrole laser physicist, Mr. David Christopher Walton Morley.
When the open end of such a resiliently deformable cylinder is mounted
on a pyramidic cone there will be four places that move in an arcuate
manner . If these arcuate movement areas have stiffeners embedded within
them, these will move out of line with any port holes that they can cover on
the pyramid faces; thus they do not reflect pressure waves.
The closed end of the cruciform membrane may have extreme thinness as
it can never see any path for extrusion or over distension. Bladders, to
contain liquid designed , proved to be extremely sensitive to pressure pulses
at up to 1000Hz.
So the HYDROCRAT broad market pump pulsation damper was born.
To force elastomers to travel the length of the above described cruciform
liquid bladders self injection “transfer pot” hydraulic to rubber intensifiers
were devised that produced rubber pressures up to 20,000psi rubber
pressure. Tools were held closed by side plate cam-locks. This tooling had
integral heating for curing the synthetic rubbers. In this novel bladder molding
operation, no presses were used. Some basic but low pressure feature of this
method were shown in UK patent 1,592,423. Granted to Liquid Dynamics Inc.
Elastomer formulation was developed by Dr. John Gardner, and extraordinary
cruciform tooling was machined by Donald Olivers company Verson Engineering.
With the benefit of exceptional elastomer formulations having typically a
600% elongation at break, 2000psi ultimate tensile strength and 55 to 65
degree shore A - and the ability to make it travel the full length of large gas
bag (bladders”) I returned to the near conventional gas bags, but to be
molded in one piece and to house them in the standard bore diameters of
schedule IPS stainless pipe for low frequency volumetric process liquids
pulsation damping . These products have been named Liquiflex and
Pipeguard. Partial copies of the smaller sizes of these have been produced
by ex employees of Hyrotrole Ltd.
Apart from superior elastomer formulation liquids compatibilities, better
physical properties, and larger sizes, the most important attributes of my
PIPEGUARDS are :
1. The anti-extrusion plate is flat, it has no central “dome” to jam off center,
propping it open for the gas bag to go around and burst.
2. Inside our gas bags, at their closed end, there are “webs” which hold it
concave around the anti-extrusion plate, stabilizing it on the center line, and
preventing premature seating before the liquid volume can flow back to the
system to maintain an overall even system velocity.
3. At he open end of the bag, inboard of the sealing bead, there is an integral
cushion ring, which prevents damage when too low a cushion pressure is set
relative to the maximum system pressure folding the bag around its header
Failure of imitations / copies of PIPEGUARD “bladders” from which important
details are missing, has caused many companies EX EG : Shell, Connoco etc
to issue specifications requiring “bladderless” dampers.
Genuine (Hydrotrole design) "PulseGuard" damper are the quality choice.
See US Patent 3308635
BLADDER , and BLADDERLESS, are terms that confuse.
A Bladder normally contains liquid, in human and other animal bodies, but is
being applied to gas containg bags, as in "balloons" or "Lungs" which contain
Stricktly speaking , neither a "Liquiflex / Pipeguard" see US Patent - Packer/
Wyley / Greer / 4,162,692 nor its "copies" are BLADDER containing devices.
They are Gas bag / balloon / lung devices.
An examples of a bladder type damper are shown in our , and a concept from
1975 UK Patent 1512000and then European Patent 0030411 September 1983
and at http://www.pulseguard.co.uk/pipehugger.html
In 1978 I prepared to emigrated to the USA and continued damper development
under the names FLOWCHEM Inc. and LIQUID DYNAMICS INTERNATIONAL INC.
See patents USA 4,098,083 4th July 1978, USA 4,162,692 31st July 1979
USA 4408635 October 1983
SIDE ISSUE - What then happend to HYDROTROLE Ltd.
The assets, copies of my Hydrotrole Ltd blueprints, customer contacts ,supplier
contacts, etc disapeared from FLOCHEM-HYDRO Ltd , and were upon information
and belief taken to "PANALGLEN Ltd" . In 1980 "FLOWGUARD Ltd" appeared,
making substantially the same product as had been at FLOWCHEN-HYDROLtd
Later FlowGuard was sold, to the WEIR Group, then from them to Hydril under
an extraordinary Name HYDRIL PCB
PCB normally means Polychlorinated biphenyl
(An environmentally toxic and classified as a persistent organic pollutant,
PCB production was banned by the United States Congress in 1979 and by
the Stockholm Convention on Persistent Organic Pollutants in 2001)
The public audited accounts of FLOWGUARD Ltd show no research and
development , Flowguard patents are not found.
The common denominator from Hydrotrole Ltd, its license to Flowchem-hydro,
transition to Panalglen, then to Flowguard Ltd are Michael Andrew Lewis and
David John Clucas.
Other "strange" manouvers occured - When Hydril the mud pump accumulator
people - holders of the "Flowguard Ltd" goodwill, were involved in takeovers -
the publicity introduced the name "Hidryl". Fearing more "sculdugery ! " i
registered the domain "Hidryl.com" .
UK Patent 1577167 May 1978, UK Patent 1249197 December 1969, USA patent
4,098,082 July 1978 - and more.