Sealey 3HP twin not building pressure

[carrera]

I was using my compressor to pump some car tyres up yesterday and after operating normally, the second time the motor engaged it just seemed to run on and did not switch off. There was a slight difference in the tone of the compressor.

It's just 2 years old and has probably got no more than 40 hours on it.

The pressure was below the usual 100psi so I switched the compressor off as it was clearly no longer building pressure.

I have had a look at it this evening and at first suspected that the overlead protector (item 41 in the parts manual http://www.sealey.co.uk/pdfs/parts/SAC10030VE_P.PDF ) as the pin was showing and I could feel some air coming out. I removed the overlead protector, removed the circlip, checked the spring and reassembled.

After draining the tank, to make easy work for it, I restarted the compressor and pressure built, somewhat slowly, to about 40psi, but no more.

Being a twin I decided to put my finger over the air intakes in turn to see if the airflow was equal. I could feel a decent amount of suction on the right cylinder, and the air was cool. On the right LEFT hand cylinder there seemed was positive pressure with hot air coming out of the intake

I took the head off but cannot see anything obviously wrong - but I'm not used to compressors and reed valves.

Any ideas what has gone wrong - I need it fixed for next weekend

Thanks in advance for any help or suggestions

 

[rtbcomp]

The overload protector, Item 41, switches the motor off if it draws too much current, and possibly if it gets too hot. If that trips the motor won't run.

If you're getting air out of the inlet then it looks like there is a problem with the reed valves and maybe the head gasket.

I'm not familiar with this pump, but I'd be looking for broken/bent reeds, damaged seats or dirt on the seats.

 

[carrera]

The overload protector, Item 41, switches the motor off if it draws too much current, and possibly if it gets too hot. If that trips the motor won't run.

You are quite correct - and I'm an idiot for referencing item 41. it's the item to the left of item 39. I'd post a picture but the compressor isn't with me at the moment.

I'll have another look at the head, gasket and reed valves, but I couldn't see anything obvious. Cheers

 

[rtbcomp]

That looks like a blanking plug on the end of the manifold. However if it has a moveable pin in it it may be a delay valve, this stays open until the pressure builds up slightly then closes. This is to allow the motor to get up to speed before it's put under load.

IIRC the closing pressure is about 20 psi, if it stays open much above this it may be faulty.

 

[carrera]

It does have a spring loaded moveable pin, so it sounds like it is a delay valve. At rest the pin is in. When running the pin is out. I didn't seem to be fully tight on the threads when I removed it for inspection and seemed to leak air. Upon reassembly there was no air leak but the compressor built pressure when I held the pin in.

I might have two problems

EDIT:

Just realised that the parts list I linked to is for the v2 of the product. I have a parts manual for the V1 that doesn't seem to be on the internet anymore. The delay valve is item 48 on the diagram and is described as "Release Valve"

 

[eil]

They normally have two gaskets one underneath the valve plate and one on top check the one on top as they usually blow.

 

[rtbcomp]

I'm still confused, item 48 is the motor fan cowl. The nearest thing to a release valve is item 73, the "safety valve".

If you PULL the pin on a safety valve it will release air, but you PUSH the pin on a delay valve to release air.

The safety valve is usually fitted to the pressure switch.

There is another valve, part of the pressure switch, called the unloader valve, this is not shown separately on the diagram, and you usually can't see it with the pressure switch cover on.

 

[carrera]

Sorry Rrtbcomp. I have two parts manuals downloaded, one for the v1 the other for the v2. The original one is no longer available online and I didn't realise that the v2 was so different when I made my first post. I have just spotted the "upload a file" button, so that's what I am going to do.

eil - thanks very much, I'm going to look at removing the valve plate this evening and will post what I find as the head gasket seems ok. When reassembling do you simply place the head components on the barrel (using grease to hold the exhaust reed valve in place ?), or do you need to assemble the head to the barrel first and then slide over the piston.

 

[rtbcomp]

Going from the PDF

48 (Release Valve): I thought this was either a blanking plug or delay valve (Post #4).

What I was calling a delay valve, they call a release valve and my description in post #7 of how it works holds good.

If one of the pistons isn't working properly the release valve most likely won't close and air coming from this will be a symptom rather than a fault.

Have a look at the gaskets as Eil suggests.

 

[normspanners]

I think you maybe have two problems too I was a little confused as to which head you have removed

Being a twin I decided to put my finger over the air intakes in turn to see if the airflow was equal. I could feel a decent amount of suction on the right cylinder, and the air was cool. On the right hand cylinder there seemed was positive pressure with hot air coming out of the intake

I took the head off but cannot see anything obviously wrong - but I'm not used to compressors and reed valves.

You needed to remove the head that had positive pressure coming out of the inlet. because that would be the faulty one

I have a similar but single cyl compressor with that same valve and gasket system
The bridge piece on the gasket blows out and stops it compressing BUT there are several gaskets to the system ALL NEED to be checked also the debris goes under the reed valves and stops them seating
mine has broken the reads on several occasions, I remade mine from pieces of feeler gauge, which has worked better than the originals

 

[carrera]

Oh gawd, I think there's just one major problem, it's me going for numpty of the month

I'll edit that post so that it refers to a problem on the left cylinder.

Thanks for the advice normspanners

Edit: It's too late to edit my first post, if a mod wants to please do so

 

[rtbcomp]

Edited - I've also reduced the image size and uploaded it as a thumbnail.

 

[thinfourth]

A 3rd voice saying take the plate off the head and look underneath it as the gasket between the head and the valve plate is probably blown

I have made them in the past from an old christmas card

And it is still working 5 years later

 

[carrera]

Edited - I've also reduced the image size and uploaded it as a thumbnail.

Many thanks

Tonights update:

I removed the barrel, inspected the piston rings, reed valves, metal gasket and valve plates. I could not see any physical damage so cleaned the components and reassembled the compressor. I did this "upside down" by placing the valve plates and reed valves on the head and assembling the barrel onto the head. I was then free to push the barrel / head assembly onto the piston using a jubilee clip as a ring compressor. Reminds me on my first air cooled VW engine rebuild, but on a smaller scale

There was no change; From an empty tank there was no pressure build until I manually depressed the release valve / delay valve. The right cylinder was sucking on the air filter, while the right one was blowing out. I could not feel any air leaks, but then again the draught from the motor fan is somwehat powerful.

I think I'll have to try a new metal head gasket and pair of reed valves, unless there are other suggestions ?

Here's some more photos. First the head & valves

And then the delay valve, assembled and dismantled

 

[carrera]

A 3rd voice saying take the plate off the head and look underneath it as the gasket between the head and the valve plate is probably blown

I have made them in the past from an old christmas card

And it is still working 5 years later

Thanks, if it was a paper gasket I would do the same, but on this model it's a metal gasket, the only paper gasket is between the barrel and crankcase

 

[rtbcomp]

..........
There was no change; From an empty tank there was no pressure build until I manually depressed the release valve / delay valve. ..............

That worries me a bit - you need to pull the pin in the release valve to close it, once closed it will start to build pressure.

When you re-assembled it did you get the head the right way round - if you get the outlet valve to inlet port it will blow straight through.

 

[eil]

Doesn't the plate that is stuck to the head not come off.
You need to check gasket no6 in your pdf.

 

[thinfourth]

Thanks, if it was a paper gasket I would do the same, but on this model it's a metal gasket, the only paper gasket is between the barrel and crankcase

Ah it is becoming clearer now

Starting at the top from memory

Cylinder head (alloy)
---------------
paper gasket
-----------------
Top valve plate
-----------------
On the same level 2 reed valves plus metal gasket
-----------------
Bottom valve plate
-----------------
paper gasket
-----------------
barrel
--------
Crankcase
---------
air tank
---------------
cheap wheels
-------------
floor
-------
Planet earth

 

[carrera]

That worries me a bit - you need to pull the pin in the release valve to close it, once closed it will start to buuilkild pressure.

When you re-assembled it did you get the head the right way round - if you get the outlet valve to inlet port it will blow straight through.

In the off position the pin is in. When the compressor starts the pin comes out, but no pressure builds until I push the pin back in again. Is this normal or abnomral behaviour ?

I was trying to get my head as to how it works. From what you say and what I looked at I think there is initially a bypass around the side of the brass plate. Then the air pressure overcomes the spring pressure the brass plate seats on the narrower bore inside the component and allows all the compressed air to flow into the tank rather than allowing some to bypass. Is that right ?

I marked the barrel and valves before disassembly to make sure that I didn't get them the wrong way round, hopefully I didn't get it wrong

 

[rtbcomp]

At rest the pin should be in under pressure from the spring. When pressure reaches about 20psi the pressure overcomes the spring and the pin should pop out. During this period you should feel a good stream of air from the valve, this air flow stops when the pin pops out. The valve doesn't divert the air.

With a faulty cylinder the air will be going from the good cylinder to the bad one and out through the inlet, but this may not happen until some pressure has built up in the manifold.

I'm at a bit of a loss as to why pressing the pin should allow the pressure to build.

Does the pin pop out again once you've pushed it in?

I take it the 'bad' piston does move up & down when the pulley rotates? Although I think a broken crank would make its presence heard!