air compressor problems

[ian of fev]

hi guys just need a bit of advice my air compressor air switch has stoped working just wondered is it still safe to use noticed the other day when i was useing it and it just kept running past 150 psi so i switched it off at the wall just to be safe there is a safty valve on the compressor will it blow off if it reaches to much presure it looks like it is adjustable now my mate has a petrol compressor when that blows off it just keeps running does it work of the blow of valve on petrol models reason i ask is my compressor is old made up of allsorts of bits and bats but ive had it 20 years now and dont realy want to spend a fortue on it if i can run it like a petrol compressor so its constantley running i can live with that just wana be safe any tips or tricks would be welcome thanks ian

 

[rtbcomp]

I would stop using it. I doubt whether those small safety valves can handle the output from the pump.

In the case of petrol compressors they have a different arrangement. When it reaches pressure a valve opens to vent the air as the engine cannot be stopped and started like an electric motor. The valve used here is not the same as a normal safety valve.

Some electric compressors have the same arrangement as petrol ones if they are being used for constant duty. The idea being to let the compressor run under no load to cool everything down rather than stop it.

 

[ian of fev]

thanks rtb actualy i was just wondering is it a simple converstion to swap it to petrol power as i was thinking of doing that thanks ian

 

[rtbcomp]

You can buy those valves, they're called unloaders and cost about £50.00 from Machine Mart.

 

[shenion]

Usually the safety valve will not open, just the compressor reaches its limit pressure. Will burn out the compressor.

A new pressure switch is not expensive and are standard. Just make sure you get one with without a dump valve.

My pressure swicth did the same. I adjusted it down and it worked for a while. Then it started getting erratic and had to replace it.

 

[rtbcomp]

....A new pressure switch is not expensive and are standard. Just make sure you get one with without a dump valve.

.....

They cost about £15.00 Why without a dump valve? Over here I haven't seen any without dump valves.

 

[shenion]

I picked up my replacement off of ebay. There are some cheap ones without dump valves.

Also check the fitting size, may be 3/8" or 1/4".

 

[ian of fev]

thanks for the replys guys if i was to convert to petrol like you say i would need an unloader valve ware would i fit this thanks ian

 

[rtbcomp]

Looking at a picture of the unloader it looks like it replaces the non-return valve that screws into the receiver and connects to the pump outlet pipe. The one in the Machine Mart catalogue has 1/2 in BSP threads.

 

[rtbcomp]

I picked up my replacement off of ebay. There are some cheap ones without dump valves.

Also check the fitting size, may be 3/8" or 1/4".

You must have one with a dump valve otherwise the pump may try to start up under pressure, this could burn the motor out.

 

[shenion]

Looking at a picture of the unloader it looks like it replaces the non-return valve that screws into the receiver and connects to the pump outlet pipe. The one in the Machine Mart catalogue has 1/2 in BSP threads.

No, there is still the check valve in the receiver. The unloader empties the pipe between the receiver and pump. Can be tee-ed in or a separate port on the compressor.

 

[rtbcomp]

This one's different then.

It has a nut & olive on the end where the pipe from the pump goes and a male thread at right angles to screw into the receiver. The adjusting screw is on the same axis as the inlet pipe so it looks like there is an adjustable unloading valve and a check valve built in.

It also has a union for the pipe to the dump valve in the pressure switch should that be used to switch the pump off.

I saw a slightly different one on a machine many years ago and that had a lever to enable/disable the unloader depending on how the compressor was being used, but I can't remember how that was plumbed in.

Look at this - this is similar to the one they sell seperately, the valve in question is next to the pressure gauge

 

[shenion]

The OP was talking about an electrical pressure switch that turns the motor on/off. You seem to me referring to a mechanical pressure release used on a gas driven compressor.

 

[rtbcomp]

The OP was talking about an electrical pressure switch that turns the motor on/off. You seem to me referring to a mechanical pressure release used on a gas driven compressor.

From the OP

if i can run it like a petrol compressor so its constantley running i can live with that just wana be safe any tips or tricks would be welcome thanks ian

 

[ian of fev]

thanks guys think i might look in to getting a new one or if not look in to swaping mine to petrol power thanks ian