Check valve with low cracking pressure

[mudandsnow]

Hello,
I am looking for a check valve with cracking pressure below 1 hPa. Do those exist? Where should I look? I have checked all the suggestions posted here: thread408-253668.

Thank you for any suggestions.

 

[moltenmetal]

What is a hPa? Did you mean less than 1 kPa? If so, good luck- that's such a tiny actuation pressure that mechanically self-actuated check valves would have a hard time dealing with it.

 

[mudandsnow]

Thank you for your reply. I want less than 0.1 kPa. The other option I have considered is using a solenoid valve. The goal is to only let air flow in 1 direction. If there is any other way to make that happen I am open to suggestions.

1 hPa = 1 hectopascal = 0.1 kPa = 0.001 bar = 0.015 PSI = 0.4 inch H2O

 

[MikeHalloran]

How much backpressure do you need to withstand when the valve is closed?


Mike Halloran
Pembroke Pines, FL, USA

 

[moltenmetal]

A weighted draft damper might actuate under such tiny differential pressure, but its reverse direction sealing will be pathetic.

Suggest you measure differential pressure and use an automated block valve, preferrably one with an external actuation means (i.e. an air- or motor-operated valve). If you try to use a solenoid valve, make sure it is a direct operated one, NOT a pilot operated one, as you have insufficient differential pressure to actuate a pilot.

 

[mudandsnow]

Backpressure is less than 10 hPa. Reverse leakage is unacceptable.

I do measure differential pressure and plan to use it to decide valve state. The smallest, lowest power solenoid valve I can find is on the verge of being too large and drawing too much power. I assume anything with external actuation is going to be larger and require more power. What is the benefit of an automated block valve over a solenoid valve?

 

[gerhardl]

Could you be more precise in size (or flow/pressure), reaction time and allowable power consumption (if motorized or solenoid operated).

The absolute no leakage requirement when closed and hence force required (back pressure pluss eventual mechanical closing pressure added) will most probably be larger than the low pressure opening force required, and works against valves operated by fluid pressure difference alone. A checkvalve with a larger exposed closing force area than opening force area could possibly help the situation.

 

[Compositepro]

For low differential pressure check valve I have used large diameter ball checks with light weight balls and also flat diaphragm check valves.

Quick-exhaust valves used to quickly dump air pressure from air cylinders also work well if they are of the flat diaphragm design.

http://www.parker.com/Literature/Li...Valve/Service_Quick-Exhaust-Shuttle-Valve.pdf

https://www.amazon.com/Parker-0R75B-Aluminum-Exhaust-Cylinder/dp/B003Q6CBHK

I cases where the standard rubber diaphragm does not have the required chemical resistance you can replace the rubber with a disc cut from fiberglass fabric reinforced PTFE film, 0.010" thick. I have used these as volume boosters for precision vacuum regulators. They have very large flow capacity for the size and they prevent process gases from flowing through the precision regulator. I see that Parker does offer PTFE options.

 

[moltenmetal]

mudandsnow: note that NOBODY in industry uses hectopascals (hPa) as a unit, even though the prefix "hecto" may exist in the SI units table. You mean that the back-pressure must be less than 1 kPa.

If reverse flow is "unacceptable", a check valve of any kind is unacceptable. A check valve is, at best, a reverse flow MINIMIZATION device. No check valve ever seals tight, unless it has been installed backwards by accident.

My recommendation stands- you need differential pressure measurement and an actuated valve. Even then, all valves leak- it's a matter of how much leakage is tolerable. With the pressures you're dealing with, there's little driving force for significant flow to occur, so that needs to be taken into account when selecting the leakage spec of any valve you may wish to use.

Overspecify a problem and you will find that it has no solution. Engineering is the art of the practical, rather than the possible.

 

[LittleInch]

Mud and snow

These pressure you're using ( agree no one uses hPa other weather people) and subsequent forces are incredibly small to make anything move either in one direction (forward flow) or reverse flow to seal it.

I think you're looking at small sizes, but even if you put in say an 8" valve with a flimsy piece of plastic at 8" you're looking at 0.75 lb force over the full area. That's so feeble a force you would need gossamer thin fabric to allow forward flow, which isn't going to give you any real sealing force even at 5 times the reverse force ( you say < 1kpA reverse flow pressure difference).

There is no way this would be a device which would meet your "Reverse leakage is unacceptable" criteria.

So go the automated actuated route if that's what you need, but again I hope you manage to find pressure transmitters to give you that level of accuracy and repeatability.

Any more info you can release on what the duty / usage is?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[moltenmetal]

1 kPa can be measured accurately and repeatably to decent resolution with a draft range differential pressure transmitter. Yes, there are some really poor quality devices of this nature for sale, but the industrial ones definitely can be made to work reliably in the so-called draft range.

 

[mudandsnow]

Thank you everyone for the help. I appreciate it. You have confirmed my suspicions that a check valve will not work in this application. I will go with an actuated valve or something entirely different.

For the record, I too prefer engineering notation (every 3rd prefix), just got stuck on hPa because that is what is used by the pressure sensor and my boss, the pressure creator