ball check valve life

[brashear]

Hi,
We want to implement a ball check valve for a small water piston pump with a service life of 50 million cycles. Is this feasible? What kind of materials and operating conditions are conducive to a long life? From what I understand, valve failure comes from uneven wear of the ball and seat. If we can keep the ball from rattling then the life can be increased?

 

[brubakerj]

Call Swagelok.
I want to say for the Swagelok 50 series, the poppet material and body material are selected in such a way that cycle failure is not a primary concern of failure

http://www.swagelok.com/downloads/WebCatalogs/EN/MS-01-98.pdf

 

[brashear]

how else could a check valve fail besides cycle failure?

 

[gerhardl]

Theoretically, assuming material and material combinations of ball and seat taken care of ('best possible' for instance high-precision polished stainless steel in combination with suitable highgrade soft sealing FKM (viton), 'Nylon', 'Delrin' or others), life will depend on material wear.

1. Material wear will again depend om abrasion. Use fine-filter to protect as best as possible, both main intake for hose/pipeline and for pistol itself. Cleaning regularily not to take too much of input pressure. (Ref best types of for instance household washing machines.)

2. Other contribution is pressure peaks. Hence pressure peaks to be damped by constructional details. Contrary to popular belief this is done by checkvalves that is closing so fast that return pressure peaks do not have time to build up to max.

Example: larger ball checkvalve with 'sidetrack' for ball, gravitational return, no spring: among the slowest and high pressure peaks possible. Nozzle check valve with spring soclled 'soft closing': already closed when delta P is zero, low or diminutive pressure peaks, well within limits.

Conclusion: High-grade ball valve to be selected. (If this is your optimum. Other constructions for soft-closing could perhaps be evaluated, conferring with producers/suppliers and application.)

Check ballvalves should at least have a firm (wear resistive) guiding for the ball, straight and short travel to close. Spring assistance?

For soft materials (elastomers): high quality to optimum grade of aldering, UV- considerations if exposed, swelling and deformation, material disformation (floating) if exposed to excess pressures (pressure peaks or perhaps possible deformation by lower or uneven pressure by fast flowing leaks through tiny crack openings when else meant to be closed)

Price/lifetime considerations, ask if supplier can give guarantee or approximate lifetime depending on cycles?

 

[brashear]

Thanks for the detailed answer. Would a hardened steel or ceramic ball and hardened seat be better for abrasion wear than a steel ball and polymer seat?

 

[brashear]

anyone?

 

[pennpiper]

Brashear,
You wrote:
"We want to implement a ball check valve for a small water piston pump "

A "Piston Pump" is normally considered a "Positive Displacement" (PD) pump. Being a PD Pump it normally does not allow back flow or suffer from the effects of back flow as a centrifugal pump would.

So my question is:
Why do you want to install a Ball Check Valve or any other kind of check valve in a situation that seemingly does not require it?

If it doesn't need it don't do it!

 

[brashear]

It's the check valves that prevent back flow. Pumps that you buy have valves installed. Since we are making our own pumps, we need to design the check valves.

 

[gerhardl]

Coming back to your question after you have given more details, I do not see why you want to select a ball checkvalve.

I could be wrong, but I believe a guided disc-type, spring-loaded checkvalve of high quality design will give you just as high flow, equal or smaller delta P, better closing performance (less pressure peaks, better sealing and lifetime. (Note: an inferior 'none precise' type of this will not give theese results).

As an example of good design and known long lifetime / perfomance have a look at the GESTRA ROCO SS series (which probably will be too large for you, but just to show the design.)

If you still wish to go for the ball-check valve: the question of ball and sealing material combination is difficult. Sometimes a softer (rubber) sealing is standing better against wear than a harder type, but aldering (over time) might be faster with the soft material.

How leakproof must the sealing be? If some leakage over time might be acceptable: leaning towards harder sealing. If to be droptight over time: leaning against softer. Reason: harder seats might perhaps easier leak across hair-thin wearmarks or deposits.

Good luck!