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hydraulic cylinder testing - "proof" test

hydraulic cylinder testing - "proof" test

hydraulic cylinder testing - "proof" test

(OP)
When a manufacturer is testing new hydraulic cylinders I would expect a pressure somewhat greater than "working" pressure would be used.  Is there a standard or common practice ( 120% ? ) that could be used as a reference?

If the "proof" pressure is known, would/should the testing include a sequence at that pressure?

thanks,

Dan T

RE: hydraulic cylinder testing - "proof" test

As a standard practice proof pressure should be 200% of working pressure and burst should be 400%. This is standard practice, however not all manufacturers stick to the same principals. Hoses, however, all should strictly adhere to this practice.

RE: hydraulic cylinder testing - "proof" test

Further info:
ANSI Hydraulic Fluid Power- Systems Standard for Stationary Industrial Machinery
(NFPA/JIC T2.24.1-1990)
Integrity(Linear Actuators)
a) Size, mounting and member strengths shall be designed for maximum expected column loads at full extension or any other limiting position withing the stroke;
b) adequate structural and/or pressure sustaining strength shall be provided for applications where overrunning or sustaining loads are encountered;
c) all load ratings shall include the mounting attachments;

NOTE - Actuators with identical pressure ratings may be not suitable for that rating with various mounting configurations.

d)when the actuator is used as a positive position stop, the actuator shall be sized and mounting selected based on the maximum incurred loading induced by the machine member restrained if this loading is greater than the loading incurred during its normal work cycle;
e) piston rod material and finish shall be selected to minimize wear and impact damage.

Durability
Performance and durability requirements shall be as agreed to between the equipment builder and the actuator manufacturer.


Source: Fluid Power Designers'
Lightning Reference Handbook
Eight Edition

RE: hydraulic cylinder testing - "proof" test

(OP)
Thanks Aces,

Does the ANSI standard mention testing of production articles?

RE: hydraulic cylinder testing - "proof" test

Hydraulic cylinder designs change to either reduce the cost of manufacture, cost of repair or increase the service life. Many manufactures only do verification testing up to 10,000 psi because of equipment and cost limitations. Pressure testing results should be less of a concern the life cycle testing results from simulations of the actual working environment.

The designs we supply will have some difference is failure pressure between bore size and working pressure ratings do to material availability limitations.

We do not have the ability to do life cycle testing but have in field performance data. When we did our seal life testing in the late 1990's at 7,000 psi we had system reliability problems that limited us to 35,000 bidirectional cycles. That was enough to prove the new design was better than the old design and get a patent. Next week we hope to start testing at 7,000 and 15,000 psi to qualify a pilot operated check valve, relief valve, rod seal design and accumulator seal design all at the same time. The rod seal and accumulator seal will be seeing 7,000 psi as will the pilot side of the P/O check. The nose of the P/O check and the relief will be seeing 15,000 psi.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: hydraulic cylinder testing - "proof" test

(OP)
I had trouble posting from my work computer, and it looks like I left out the info that the actual "working pressure" is around 3500 psi, and the "proof pressure" on the drawing is listed 4500 psi or so.  The outfit that made the new cylinders only tested them to 3500.  My question is should they taken each new cylinder 10% over, to ~ 3850, or to 4500?

My first expectation is a new cylinder should be tested at some pressure > working pressure.

RE: hydraulic cylinder testing - "proof" test

Unless you specify a testing pressure most cylinder manufactures will limit the test to between 3,000 and 4,000 psi because of equipment limitations. Testing over 4000 psi requires a piston pump, more expensive valves, hoses and guarding.

If you have specified a 3500 psi working pressure you are probably getting a 3,000 psi cylinder and the seals used will degrade some just testing to 4500 psi. The manufacture may have qualified the design to a higher pressure but will limit the production testing pressure. We use the testing after assembly to check for leaks and blow by and limit it to the working pressure or 4,000 psi even on our 6,000 psi cylinders due to equipment limitations. We are upgrading the testing to 5,000 psi maximum later this month.

Ed Danzer
www.danzcoinc.com
www.dehyds.com

RE: hydraulic cylinder testing - "proof" test

The hydraulic cylinder company I use has their cylinders rated as working pressure and max. non-shock pressure.  For example, a model X cylinder will have a 5,000 psi working pressure and 8,000 psi max non-shock pressure.  In other words, they tested to 8,000 psi, but to maximize the life of the cylinder the working pressure is rated at a much lower psi.  Similar to automobile companies rated oil changes at 7,0000 or 9,000 miles, changing it at lower miles is better for the life, but it wont hurt too bad to go longer.  
  

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