Pressure relief Valve.

[Aston66]

When new, with no internal corrosion, no fatigue from a million pressurisation cycles and no dents etc, it will have been safe at 15 bar if that's what the plate says. 30 years later having been sat half full of water and gunk it's anyone's guess. It may only have a fraction of the material thickness left at the bottom.


If your lucky, if not its goodnight Vienna!


I tested hundreds of PRVs of various types in a previous job and whilst they were often a bit off, especially when old, they were generally fairly accurate. Where are you measuring your pressure from, and where is your PRV situated? On the tank or on a feed/ take off line?

Are you sure it's the PRV letting go that's stopping you reaching the pressure you want and not the compressor failing to reach it or something else letting go. I've seen compressors with multiple PRVs.

As @addjunkie said earlier if your compressors old and knackered it may not ever get to its original design pressure, let alone more.

If your finding numerous PRVs are all low then I'd suspect your gauges, or where your actually measuring your pressures from to be the issue. Get yourself a bucket pump and test them against a known good gauge.

Hi. I'm measuring the pressure from the tank. I have recently rebuilt the pump unit and the pistons, cylinder bores , valve plates etc appeared to be in surprisingly good condition for a ' cheapo Oriental' machine after 12 years of use.
The check valve and unloader valve also function correctly.
The pressure switch unloader valve works as it should too.
It does begin to look like all my gages are Knackered. It's the only conclusion that makes any sense, I shall buy another Guage and see what it reads .
I would not like to run this compressor over it's safe working pressure, Wich is obviously why I'm so concerned about the PRV , in the case that the switch does fail. Usually I keep an eye on it any way, when I'm using it, to be frank, I don't trust it since it dropped a Conrod. It gets drained down every time I'm finished with it and I don't think I have quite managed to exceed it's duty cycle yet.
I have been led to believe that the receiver, should accommodate a PRV of 10% of more than safe working pressure. That the 15 Bar figure is a pressure test figure with water and that the figure at which the receiver breaches is probably up to two times that figure ???
I've read that amongst posts on this very forum.
However I certainly don't want to try to achieve anything over 145 psi.
I guess that I should take heed of the advice given to me in this thread, and stop ' pushing ' the capabilities of this Knackered old piece of Asian manufactured junk.

 

[8ob]

A question for the safety valveists, are these valves a progressive release as in will they will start to partially release at below the max so they are fully open at the rated max. just thinking there must be a differential between open and closed because at the end of the day its only a spring and plunger.

Bob

 

[brightspark]

they progressively open and close as the pressure changes. they dont just blast off when up to operating pressure

 

[brightspark]

they progressively open and close as the pressure changes. they dont just blast off when up to operating pressure

 

[AVI_8]

If it’s operating pressure is 10 bar and the safety valves are opening between 8 and 9 bar that‘ll mean that the motor will run continuously and not shut off as it’s not reaching its operating pressure, is that’s whats happening.

 

[bricol]

Any way in the event of failure, it would likely be a ' Pin Hole' in the receiver due to internal corrosion.
They don't just ' blow up as in all these YouTube videos.
I ll take my chances

I like your confidence, I'm not sure what its based on though . . .

I'm no expert , not an engineer etc' I

They can and do let go, although reasonably rarely.

 

[Aston66]

If it’s operating pressure is 10 bar and the safety valves are opening between 8 and 9 bar that‘ll mean that the motor will run continuously and not shut off as it’s not reaching its operating pressure, is that’s whats happening.

Not quite. The pressure switch was set to cut out at about 140 psi, near enough to 10 Bar. The pressure relief valve starts to vent at about 8 Bar, push it back in and it will go up to about 9.-9.5 Bar before fully opening. Obviously, I switch it off then as it's just venting air to the atmosphere and as you say, over working the motor and pump.

 

[Aston66]

A question for the safety valveists, are these valves a progressive release as in will they will start to partially release at below the max so they are fully open at the rated max. just thinking there must be a differential between open and closed because at the end of the day its only a spring and plunger.

Bob

I'm learning a bit more about them now, never really had to consider them much before this problem.
The valves I have are all pistons tensions down into a bore with a spring , the spring is held captive with a threaded screw cap, through which the end of the piston rod protrudes on the non pressured side. They look quite simple. I have been thinking whether these type of valves vent gradually or at reaching a certain pressure.
It does look as if they work on a gradual increase of pressure on the piston, compressing the spring.

 

[Aston66]

I've seen you tube videos of it happening and the aftermath. It's often the case on further investigation though , that they have been recklessly modified , repaired,( I.e. welding repairs on tanks by amateurs etc)
Or have been unattended and unmaintained.

 

[Pete.]

I wonder if pulses from the pump are momentarily pushing up the pressure and cracking the valve? If they have tested it from a static supply at 11 bar or whatever that might explain the discrepancy (or their gauge might be duff).

You say that if you hold it closed with your finger to 9.5 bar it opens fully. Does it do the same if you shut the motor off?

 

[Aston66]

I wonder if pulses from the pump are momentarily pushing up the pressure and cracking the valve? If they have tested it from a static supply at 11 bar or whatever that might explain the discrepancy (or their gauge might be duff).

You say that if you hold it closed with your finger to 9.5 bar it opens fully. Does it do the same if you shut the motor off?

Spot on.I was thinkinking that my self earlier! Perhaps it a fault in the ' One way valve', your thinking good.

 

[Screwdriver]

What you really need is a larger receiver. If everything else seems to be working ok, 90 litres is a bit of a tiddler and even ramping up the pressure won't maintain your desired cfm for that much longer.

 

[Aston66]

But if I got a larger receiver, would I not need a larger pump also?
I had to rebuild the B,3800 pump on this because a new pump costs just over half the price of a whole unit.
B3800 pumps are getting scarce! And expensive. Home compressors are mostly direct drive V Twins with allot cylinders. The Wolf is a Vertical Twin with cast Iron Barrels and belt drive .
The B3800 is a long stroke pump as apposed to the more popular B2800 modles or copy's. They need to run at a much higher RPM to achieve quoted FAD.
Not a good combination.
Adding a larger receiver will just shorten the life of both pump and motor.
Thanks though, it's all a learning curve for me.

 

[Aston66]

But if I got a larger receiver, would I not need a larger pump also?
I had to rebuild the B,3800 pump on this because a new pump costs just over half the price of a whole unit.
B3800 pumps are getting scarce! And expensive. Home compressors are mostly direct drive V Twins with allot cylinders. The Wolf is a Vertical Twin with cast Iron Barrels and belt drive .
The B3800 is a long stroke pump as apposed to the more popular B2800 modles or copy's. They need to run at a much higher RPM to achieve quoted FAD.
Not a good combination.
Adding a larger receiver will just shorten the life of both pump and motor.
Thanks though, it's all a learning curve for me.

What I need is a good PRV. That does what it is supposed to do, and possibly a good Guage.

 

[DanZac]

Adding a larger receiver will just shorten the life of both pump and motor.
Thanks though, it's all a learning curve for me.

It'll be the same as your plan to increase the pressure, take longer to fill the receiver in the first place, but kick in less often and you'll have more air available, which is what your trying to achieve.

Swings and roundabouts as they say.

 

[Aston66]

It'll be the same as your plan to increase the pressure, take longer to fill the receiver in the first place, but kick in less often and you'll have more air available, which is what your trying to achieve.

Swings and roundabouts as they say.

I hear you' it is a case of ' swings and Roundabouts' as you say.
I like people who think out the Box.

 

[pedrobedro]

they dont just blast off when up to operating pressure

Mine does on my Wolf compressor, it doesn't half make you jump

 

[brightspark]

Mine does on my Wolf compressor, it doesn't half make you jump

it makes a bigger bang when a flexible hose blows up like a balloon behind your backside and bursts

 

[Screwdriver]

It'll be the same as your plan to increase the pressure, take longer to fill the receiver in the first place, but kick in less often and you'll have more air available, which is what your trying to achieve.

Swings and roundabouts as they say.

yes and on the swings we have a larger receiver, the roundabout is hacking the pressure relief to overdrive the compressors….

I would be wary of pushing the pressure envelope on a smaller tank compared to just getting more air from a bigger one. Bit like upping the fuse from 5A to 13A to stop your widget from blowing fuses.

 

[addjunkie]

I think based on experience the bigger tank will extend the life of the rotating parts. As there is more wear and tear when they stop and start. With the larger tank itll all run longer but cut in and out far less. If your planning to paint the bigger tank is a must for quality work