Pressure relief Valve.

[Aston66]

Hello. This week I have bought two 11 bar Pressure relief valves for my compressor. Both of them have started to blow off at between 8 and 9.5 bar. I'm getting really frustrated now as I would like to run my compressor up to 10 bar working pressure, Obviously test pressure is higher, 15 Bar according to plate.
Can anyone recommend a suitable valve or a company who could sell me one?
I have tried three different pressure gages and they all read the same when the valve releases .
I may be over looking something ? as the company who sold me the 11Bar valves assure me they tested it to 11.5 Bar before sending it out .
To be fair they have refunded me fully and quickly , but I don't won't to waste any more time or money with similar products.
Any advice welcome.
Thanks.

 

[Moose McAlpine]

Do you have pictures? Are they not adjustable? How are you reading the max pressure? (Tank gauge?)

I've adjusted the cut-off on my compressor, it has a simple adjustment screw, and the relief valve on it appears similar.

 

[Aston66]

I'm talking about the Pressure Relief Valve, or safety valve which prevents the over pressurizing the receiver.
This is a separate component to the pressure control switch.
The switch works as it should' ( up to a point, cheap ebay item not very adjustable or reliable)
The valve I'm talking about is the ' fail safe' in the event that the switch it's self fails.
Thanks

 

[Moose McAlpine]

I know, but was wondering if it may have some kind of adjustment, as if so it will work on the same principle (spring pressure) as the cut off.

 

[Aston66]

It doesn't look like it's adjustable, but I believe some are. It's the standard plunger type with a split ring through the end, and I don't think it's adjustable, at least I can't see a way of adjusting it? I have been reading the pressure direct from the tank with three different gages , and they all indicate the same ' blow off pressure.

 

[Moose McAlpine]

Does it have a slot in the end, where the pin and ring pass through?

 

[Aston66]

Yes it does. Can that be adjusted?

 

[Aston66]

Yes it does. Can that be adjusted?

I was thinking about getting a Pin spanner or making stool, to see if I could tighten or loosen that, to see if it made a difference's I suppose I should try to tighten it, to increase the pressure on the spring yes?

 

[Moose McAlpine]

I was thinking about getting a Pin spanner or making stool, to see if I could tighten or loosen that, to see if it made a difference's I suppose I should try to tighten it, to increase the pressure on the spring yes?

Yes, tighten to increase. (At your own risk.)

Wonder why they had it open at 11, but you've had it open at 8-9. Very odd.

 

[Aston66]

I know? Not just 1 but two. Here's a photo of one of them.
I can't see all three of my pressure gages being wrong?
But as you say I don't like taking to many risks with compressed air cylinders.
I'll have ago at tweaking it in very small incruments and see how it goes.
Thanks for your advice

 

[Aston66]

I reckon they have tested a few of a batch and they have been mis labeled, and entered into stock at the wrong rating.

 

[Ross365]

Some PRV are certainly adjustable, but I don't know about the "budget" priced ones as in the picture. It's sometimes done using different springs (colour-coded) together with an adjustable top cap. My recollection is that may compressors have a limit of 8bar on the tank, so no surprise that there are 8bar PRV's. For quality PRV, I go to Swagelok, but they are pretty expensive.

 

[Aston66]

Safe working pressure is 10 Bar, PT is 15 Bar, on my compressor. The switch and PRV it came with are damaged, diaphragm has burst and the spring in the original PRV seems to have given up .
The switch I bought off eBay was a joke, supposed to be adjustable up to 175 PSI, in reality it doesn't work after 125PSI.
But the two PRVs I bought this week where listed as 11 Bar, and won't hold 11 Bar. It's giving me a head ache.

 

[Ross365]

It's giving me a head ache.

Yep... but definitely worth getting it right. When you see pictures of compressor tanks which have burst (even at 8 or 11bar) , it looks like a bad experience! The firm I used to work for tested 700 litre light-weight titanium tanks to 15bar. It was done in a concrete bunker which had WWII submarine nets as a 'roof'.

 

[winchman]

They do look like a cheaper variety, in my experience and having tried several suppliers this is the best and most knowledgeable, but like all things cheaper ones are available as you have found out.

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[DanZac]

Without wishing to be all H&S I'd suggest that before you start adjusting them, it's worth getting a certificated pressure relief valve (there's a big difference between "yes we've tested it" and an actual certificate), or test your gauge against a known good (calibrated) one to ensure it is correct.

The last thing you want is an air receiver failing.

 

[addjunkie]

Might one enquire why you want to increase the operating pressure upto 10 bar?

 

[Aston66]

Might one enquire why you want to increase the operating pressure upto 10 bar?

Its a 90 ltr , 3 HP, 9 FAD, compressor. I find that at 125 PSI , the differential in pressure is to wide and lose pressure quickly. I found I could get a more constant 100- 90 psi having a higher cut in point.
I like to pump it up to 145psi, and let it cool for a bit, it seems to leave most of the water in the tank that way. I do this when I'm using a spray gun or home made grit blaster.
I know it uses more energy and , places strain on pump and motor etc, but I only use it occasionally.
I hear differing points of view on this subject, What is you thinking.

Without wishing to be all H&S I'd suggest that before you start adjusting them, it's worth getting a certificated pressure relief valve (there's a big difference between "yes we've tested it" and an actual certificate), or test your gauge against a known good (calibrated) one to ensure it is correct.

The last thing you want is an air receiver failing.

I'd like a certified one.
I'm thinking I don't want to spend to much on what is essentially a ' hobby'. It sits in the shed most of the year. It's getting old and Will need a new pump at some point. I've already rebuilt the pump and it's at that point where you repair on component then the next component fails.
I think I may just go along to my local MM and buy one of their generic switch gage and PRV sets and run it at 125 psi.
Thanks.

 

[graffian]

I have a few Norgren ones, they are probably the same as the one you pictured except the body and cap has a locknut so you can alter the spring tension.
You could add a shim to the spring in the one you have, it will be a bit more laborious to set than a threaded one but will do the same job.
Heres a pic of a nice shiny valve.

 

[Aston66]

That looks very much more engineered than the ones I have.
I like that