compressor problem

[eaglesalz]

Hello all,

I have a old Sip compressor has worked fine for many years, dropped a bit of wood on the unloader/pressure switch which broke the plastic cover but still worked for a few more years, but recently it now tries to start, a bit like turning your car over with a flatish battery and then trips the breaker (16amp). Decided to put a new unloader switch on but still the same (do you have to adjust these for pressure?), the only difference now is that it does not trip the mcb but the main switch, the compressor is single phase and the motor is a hawker sidley on the plate it draws 15amps. Would a capacitor on the motor cause this (there are two). Thanks in advance.

 

[doctor Bob]

We used to have a couple of big SIP's, replaced the capacitors fairly regularly on them, pretty sure this is the problem.

 

[dizjasta]

How is the oil in the compressor? Can you slack the drive belts and see if the motor starts on its own? Also with slack belts are both motor and compressor turned easily by hand?

 

[sunnybob]

Capacitor is most likely.

 

[eaglesalz]

We used to have a couple of big SIP's, replaced the capacitors fairly regularly on them, pretty sure this is the problem.

How do I know what capacitors to get, they have no markings on them.

 

[eaglesalz]

How is the oil in the compressor? Can you slack the drive belts and see if the motor starts on its own? Also with slack belts are both motor and compressor turned easily by hand?

Oil is on the mark, never thought of taking the belt off, so I have just done that, both turn freely and when I turn the compressor I can hear the valve/pressure/unload switch making a hiss when I turn. Also the motor starts up fine when no belt is on.

 

[eaglesalz]

I have just dumped all the air out and it fills up and switches off, but if I switch off the motor whilst it is filling or halffull and switch it back on it goes into it's "oh do I have to start up again mode". It's like me when I try to get up in the morning (and I mean get out off bed).

 

[eaglesalz]

There are two capacitors on the top of the motor, would the run capacitor still work if no load on the motor and when I connect the belt it struggles?

 

[dizjasta]

If the load is taken off the compressor by leaving the receiver drain cock open does the motor start and restart after being
switched off manually?

 

[eaglesalz]

If the load is taken off the compressor by leaving the receiver drain cock open does the motor start and restart after being
switched off manually?

Yes, if the drain cock is left open it does start, and when I stop it (with drain cock open) and start it again it is fine. As said, I have put a new switch/pressure on but still no joy. I was wondering if the start capacitor is faulty and when underload it just does not do it, but if I take the belt off the motor works fine.

 

[doctor Bob]

We used to have a couple of big SIP's, replaced the capacitors fairly regularly on them, pretty sure this is the problem.

How do I know what capacitors to get, they have no markings on them.

We used to remove and take to local motor shop and they would replace with like. seem to remember you can get 4 wire or 2 wire ones.

 

[eaglesalz]

We used to have a couple of big SIP's, replaced the capacitors fairly regularly on them, pretty sure this is the problem.

How do I know what capacitors to get, they have no markings on them.

We used to remove and take to local motor shop and they would replace with like. seem to remember you can get 4 wire or 2 wire ones.

One capacitor is in a plastic case and the other is in a aluminium case, sip have sprayed the motor and all it's houshings black, along with the capacitors, I thought it might be a case of the motor is this size/power and this is what capacitors are needed, but apparently it's not that easy.

 

[wallace]

I've got a sip compressor that's not been playing nice recently. It used to blow the fuse in the plug during the winter but now it seems to be blowing it a lot more regularly. It blows on first start up. I was going to wire it directly to an mcb. Any ideas.
sorry for the hijack

 

[dizjasta]

eaglesatz the way your SIP compressor is acting suggests that pressurised air from the receiver is leaking through the reflux valve into
the cylinder. This valve will be located on the pipework connecting the receiver to the compressor and can be serviced or replaced. When
working properly it ensures that the induction motor can start with little resistance to develop torque and run easily. In most cases the valve is a flap or poppet held closed by a light spring.

 

[dizjasta]

wallace what is the rating of the fuse you are replacing? It sounds like there is high resistance somewhere. You need to check all connections at plug and motor box. In your position I would renew the plug, fuse and power cord. The environment in workshops tends to be hard on electrical parts.

 

[eaglesalz]

eaglesatz the way your SIP compressor is acting suggests that pressurised air from the receiver is leaking through the reflux valve into
the cylinder. This valve will be located on the pipework connecting the receiver to the compressor and can be serviced or replaced. When
working properly it ensures that the induction motor can start with little resistance to develop torque and run easily. In most cases the valve is a flap or poppet held closed by a light spring.

I took (what sounds like what you said) off (big pipe from compressor, small copper pipe to pressure switch) and it seems to be fine, but then I don't know what a good one would look like, it had a very light spring in it and the rubber was like one off the old type of tap washers (minus hole) about 4/5mm thick. The spring did look a it weak though.

 

[dizjasta]

The seating for the rubber needs to be checked for corrosion of rough spots and cleaned up if necessary. A light spring is all that is needed but if your feel it has been weakened or corroded look for a replacement, SIP perhaps. Check the rubber for ridges or lost material and install it reversed. It is possible debris was holding the valve open which has fallen away but may still be in system. Put everything together and retry. Start the compressor and allow it to reach pressure and dump valve to operate. Disconnect from supply. With ear close to unit listen for leaks. If leaks are detected new parts will be needed.

 

[wallace]

Thanks for advice, I've always thought having a 3hp running from a 3 pin plug is pushing it. My compressor is kept in a lean to to keep the noise down in the shop. It is kept switched on and I just use the socket switch for on/off. It maybe needs a bit tlc its been in there for about 7 years