3hp air compressor problem

[pauls440]

Hi all I have a 3hp air compressor with a new pump was working fine, but now it trys to start but won't turn over, if I move the motor so it's lose it will start and then I tighten it up it works the pump but as soon as the pressures drops and it gos to fire up it stops.
Could this be the starter maybe ????

Any help would be appreciated

Paul

 

[ford34/2]

unloader valve not operating, pump trying to start against the pressure in the Tank??

Stan

 

[pauls440]

Hi Stan thanks for your reply but can you tell me ware that is please

 

[roofman]

Hi Stan thanks for your reply but can you tell me ware that is please

its in the pressure switch mate,the black box type...has a thin pipe that runs from the off-loader to the 1 way filling valve

 

[pauls440]

Ok cheers just replace it then

 

[roofman]

Ok cheers just replace it then

or it could just be sticking...do you drain the water out the tank on a regular basis

 

[rtbcomp]

When it stops can you hear a brief hiss?

 

[pauls440]

Roofman yes I do thanks.

Rtbcomp what I was spraying the next thing was a big hissing noise and there was lots of air coming out of the bottom of the black box.

 

[roofman]

Roofman yes I do thanks.

Rebcomp what I was spraying the next thing was a big hissing noise and there was lots of air coming out of the bottom of the black box.

As the detective said.."sir were going to have to detain you as there has been more evidence brought forward"

 

[pauls440]

So is that the unload valve gone then

 

[roofman]

So is that the unload valve gone then

see iff the pipe has come off...normaly held on by a very small brass olive and threaded collar or another type is a push fitting

 

[pauls440]

Hmm but when I run it up it goes to pressure just won't restart

 

[rtbcomp]

Normally you just get a brief hiss, if it's continuous then the non-return valve (NRV) is allowing air to leak past it. This is the thing that connects the pipe from the pump to the tank, and has a thin pipe going to the unloader valve.

The unloader valve is probably OK.

Drain the tank completely and screw the large nut off the back of the NRV, you may get away with giving it a good clean.

 

[roofman]

Hmm but when I run it up it goes to pressure just won't restart

yea at ist its starting with no pressure so pretty easy....then it might click off at 100psi when full and re-start again as it falls to 75psi and its this point that without the off-loader the motor cant cope

 

[pauls440]

Ok will try this and let you know

 

[rtbcomp]

 

[pauls440]

Ok will buy a new one and check the nrv

 

[ford34/2]

Your reciprocating piston compressor will have a smooth start up, thanks to the unloader valve.

The air compressor unloader valve is a small, but important, part of the reciprocating piston compressor. It blows off the pressure inside the discharge pipe when the compressor stops.

The output of the piston compressor is connected through a pipe to the air receiver. When the compressor stops, the pressure in this pipe is blown off to 0 bar (atmosphere).

This is the ssssssshhh sound you will here when the compressor stops. At the same time, a check-valve makes sure that not the whole air receiver (tank) flows empty, but only this small pipe.

Why? When the compressor starts up again, and this pipe would still be under pressure, the electro motor will not be strong enough to turn the compressor.

If you google unloader valve there are many pics, it will probably be part of another bigger valve pressure regulator setup.

Maybe pump up the compressor till it trips off at full pressure, empty the receiver, start up again, if it starts it would appear the motor and pump are performing ok, if it doesnt like to start up from empty, points to Motor/pump fault. if it wont cut back in when full pressure drops down, still points to unloader valve stuck . You do hear a good sssssssssssssHhhhh as it stops when reaching full working PSI

 

[rtbcomp]

Ok will buy a new one and check the nrv

Check the NRV before buying anything!