Free Floating Piston™

T H O M A S S E NC O M P R E S S I O N

S Y S T E M S

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Free Floating Piston™

Revolutionary reciprocating It is now more than a century ago that Mr Thomassen first began to

make gas engines. He soon extended his activities to include the design

and production of reciprocating compressors and what started out as a

small, local company has grown into a major compressor supplier with

sales outlets and service at strategic points around the globe.

Thomassen Compression Systems (TCS) supplies heavy-duty recipro -

cating and oil-flooded screw compressor packages as well as rerated/ -

rebuilt centrifugal compressors. In addition, we offer full service,

installation, spare parts and repairs, maintenance and troubleshooting,

round the clock, all over the world. Exports currently account for more

than 80% of sales and our customers include oil refineries, gas & oil

exploration and production companies, and petrochemical plants.

The weakest

point becomes

the strongest

R i d e r r i n g w e a r

Due to ever more stringent environmental regulations,

there is a trend towards the use of non-lubricated com-

pressors. Such machines, however, require increased

maintenance because rider ring wear is unpredictable.

Indeed, certain process and gas conditions accelerate

wear so drastically that running time can be reduced to

as little as a few hundred hours. Given today’s com-

mercial pressures - that dictate running times of three

years or more - this situation clearly presents owners

of compression systems with a problem….

A n e l e g a n t s o l u t i o n

TCS has come up with an extremely elegant solution.

A design that virtually eliminates rider ring wear

by allowing the piston to float freely on process gas.

The advantage of this revolutionary idea is that wear

only takes place for very short periods during startups

and stops.

This development removes in one stroke the weakest

link in the chain as far as compressor component failure

is concerned. What’s more, the full benefits of increased

lifetime of other parts that are subject to wear can now

be realized. The industry’s requirement for at least

three years of uninterrupted running time with non-

lubricated cylinders is finally within reach.

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compressor design

E n v i r o n m e n t a l c o n s t r a i n t s

The design of Thomassen’s reciprocating compressors

- which are custom-built and meet or exceed API 618 -

is based on the horizontal balanced opposed type. If

the moving parts are lubricated with oil, then wear is,

in general, acceptable. However, when the type of

process gas or environmental regulations dictates that

the piston must be supplied non-lubricated, wear

increases dramatically. In some cases this action is

similar to that of an eraser. So non-lubricated compres-

sors need regular maintenance and a second back up

machine is usually essential to ensure the levels of

availability required in today’s production processes.

R e s e a r c h - l e d r e s u l t s

One approach was to attempt to improve the proper-

ties of the rider ring/liner materials. However, so far

this has only produced marginal improvements.

Thomassen took another approach - one that was

much more fundamental - to rethink the basic principles

of compressor design. A feasibility study covering the

full range of construction principles led to the creation

of a revolutionary new design, which equips the piston

with a gas bearing:

The Free Floating Piston™

T o l u b r i c a t e o r n o t t o l u b r i c a t e

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Top view measured pressure distribution

Top view calculated pressure distribution

Side view measured pressure distribution

Pressure vs time measurement

N o c h a n g e i n c a p a c i t y

The bearing layer between the rider rings and the cylin-

der liner is in the order of 10 to 50 microns, and the

flow required to lift the piston is less than one percent

of the compressor’s capacity. The new construction

compensates for this, so net compressor capacity is

the same.

R i g o r o u s t e s t i n g

The system has been subjected to rigorous static and

dynamic testing on Thomassen’s in-house heavy-duty

test air compressor. This was followed by a successful

pilot test in a heavy-duty production hydrogen

compressor at a customer’s site.

A c t u a l E x p e r i e n c e

The first compressor to be fitted with our Free Floating

Piston™ has meanwhile clocked up more than 60.000

hours of trouble free operation.

The principle of the Free Floating Piston™ technique is that the weight of the

piston is carried by the process gas itself.

During the compression stroke, the interior of the piston is filled with process

gas at high pressure.

Due to the pressure difference, the process gas flows out at the bottom of

the piston, ensuring that there is no physical contact between rider rings

and cylinder liner.

No friction

As a result, rider ring wear is reduced to practically zero, resulting in

substantial increased rider ring lifetime.

The design of the piston itself has been adapted as follows:

• to create constant pressure, the rider rings have been relocated

between the piston rings

• regular compressor valves that react to differences in gas pressure

have been installed in the piston faces, enabling gas to enter

the interior of the piston

• flow nozzles have been integrated in the rider rings and a profile machined

on their lower surface to create a bearing layer under the piston

Fail-safe

How does it work?

• practically no rider ring wear

• increased lifetime of piston rings

and stuffing box elements,

due to the piston maintaining

its centralized position

• no lube oil pollution of process

and valves, no cylinder lubrication

system, no lubrication costs

• reduced preventive maintenance

costs (time and materials)

• reduced production losses

• increased reliability and

availability

• a major reason for having

a spare compressor is eliminated

• suitable for all kinds of

process gases

• the design can be applied

to existing compressors

• no risk (fail-safe)

• lower power requirement

• lower sound levels

K e y a d v a n t a g e s o f t h e F r e e F l o a t i n g P i s t o n™

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Putting the principle into practice:

Thomassen Compression Systems’

Free Floating Piston™ technology

Putting the principle into practice:

Thomassen Compression Systems’

Free Floating Piston™ technology

T H O M A S S E NC O M P R E S S I O N

S Y S T E M S

Head Office

Thomassen Compression Systems

Havelandseweg 8-a

PO BOX 99

6990 AB Rheden

The Netherlands

Tel: + 31 26 4975200

Fax: + 31 26 4975201

E-mail: tcs@thomassen.com

www.thomassen.comFor Service Operating Companies, Sales Offices & Agencies, please visit our website.

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