Compressor won't start.

[T i m]

Hi All,

I'm going through my compressors atm and have the following question.

The little Bambi 75/150 silent jobby won't re-start once up to pressure. It looks like it tries but I think the control unit backs it off if it doesn't.

From memory I *think* it's better if not on a long lead but I'm sure that shouldn't matter as it's only a small wattage compressor.

Now I'm not sure what's *supposed* to happen on *this* compressor (it's been a while since I last used it) but when it's reached pressure it shuts off ok but with no "pschtt" like the other two do AND when it does shut off the air leaks back very slowly and I think it sounds like it's coming back into the compressor pump (it's all sealed so I can't be sure).

So, if it's supposed to have a pump pressure release valve (and I'm wondering if it is as that would stop it being 'silent') I wonder if it's stuck / leaking and if so, is it something that could be cleaned / serviced (by me) do you know please?

It's similar to this:

the best ..

T i m

[Harry Bloomfield]

T i m formulated the question :

Certain compressors are fitted with a valve which both stops the compressor once it is up to pressure and allow it to start against no compressed air load, until it is up to speed.

[Andrew Gabriel]

Could be trying to start with compressor outlet already presurised when not designed to do so, or could be that the start or run capacitor for the motor has died, which will result in reduced starting torque (or none at all if it completely dies).

[T i m]

Indeed and I think what I was eluding to above Harry but because I got this second hand a long time ago, haven't used it much in the meantime and don't have a manual for it I'm not sure what it's supposed to do (I know what my other two compressors are supposed to do and they both do it) ;-)

The reason I'm not sure if this Bambi jobby is designed the same is because it's a quiet as a fridge in operation (they are used extensively in dentists etc) and a nice loud "PSHHHST" every time it reaches pressure might defeat the 'silent' badge a bit?

I might give them a call and see what they say before I look at it closer myself.

All the best ..

T i m

[T i m]

That was one of my thoughts Andrew, reinforced by what I *think* is it leaking (de-pressurizing) back through the pump (I'm pretty sure it's not leaking elsewhere).

Ah, now there's a thing. I've got a funny feeling I've already replaced that but it was a long time ago. The compressor hasn't been used much since then so I wonder if these caps 'dry out' or need forming (or is that only for DC use?) etc?

The last time I worked on a problem with this little compressor I believe it would start if plugged directly into the wall socket but not of on an extension lead (and how I tried it last)[1]. As it's not raining now I'll drag it out and try it both ways again and see what happens.

All the best ..

T i m

[1] Only about 5m and very thick cable. I use it on my ARC / MIG welders.

[Bob Minchin]

Fridge type sealed compressors don't use capacitors to start in my experience. Instead a current controlled relay in series with the run winding, sense the stalled current and switch in the starter winding in parallel with the run winding until the current drops and the motor is running. The whole arrangement is protected with an auto resetting thermal cutout in the event of motor failure ans possibly in this case, starting into a high pressure load. In normal automatic operation in a fridge or freezer, the compressor is never required to re-start until the pressure has dropped.

Bob

[T i m]

Hi Bob and thanks for that (interesting).

I'm not sure if this is that type of compressor. I spoke to their T/S today and he kindly sent me a manual with exploded and wiring diagram.

This one (if different from a fridge) is a little piston compressor with some of it's moving bits in a bath of oil?

He suggested it (as I thought) it didn't have a 'dump valve' (the thing that normally goes 'pchsst' when it reaches pressure) but the pipe from the pump and non_return_valve would normally drop to atmospheric pressure between stop-start phases, giving the pump a chance to spin up a bit (pressurizing the air in the pipe from pump to reservoir) when starting at pressure.

He also suggested therefore the issue might be the non_return_valve, leaking slightly and this is not untypical.

I removed it and stripped it down earlier and although there was a bit of gunge in there it wasn't 'terrible' (mind you, it only needs a spec of stuff in the seat I guess).

I'll pop down the workshop later, put it back together and see what happens .

All the best ..

T i m

[T i m]

No force with me tonight it seems. :-(

In spite of the valve being visually clean it still leaks when on the compressor and even when I blow through it?

I know it might need a bit of back pressure to really close the valve but the actual valve part is a rounded rubber cone sprung loaded onto a conical seat so you would have thought it would sealed pretty easily.

Apparently they are only 15 quid so it wouldn't be a show stopper if I had to replace it (apparently we have a Bambi dealer pretty local so I'll find out tomorrow). I need some fresh oil and an intake filter in any case so ...

All the best,

T i m