Air compressor connection issue

[Dean1983]

Hi there,

I have a 2 HP Sip Cosmo air compressor.

I wish to replace the existing manifold/pressure gauge assembly as it is old and obsolete and doesn't contain an output gauge. It also has the regulator built in to the manifold which has failed anyway.

I have purchased a pressure gauge, new pressure switch and regulator with gauge but I am stuck on one part.

From my research, usually the outlet from a tank to the pressure switch is 1/4 bsp female and using a short 1/4 bsp male nipple I can connect the tank to the pressure switch.

In the case of the Cosmo I've found that the tank outlet is a collared neck with a rubber seal and the old manifold containing a tapered grub screw to hold the manifold to the neck. See attached pics. Sorry they are upside down. I tried to change that.

Does this make sense to you guys?

I'm thinking of having the collared neck cut off and some sort of 1/4 bsp female nut welded to the tank. But how do I empty the tank of swarf after?

This is a drastic measure and I'm not sure it will work. Is there some sort of fitting to convert my neck collar to a 1/4 bsp female? I'd rather not commit to cutting and welding.

 

[Dean1983]

Just to add, there is no thread under the rubber seal. Either male or female.

 

[rtbcomp]

Welcome to the forum, I've put the images the right way up.

I'd be inclined to cut the original fitting off and braze a threaded union in place.

Use a hacksaw with plenty of grease on it to catch swarf.

Are there any other ports on the tank you could use?

 

[Dean1983]

Hi and thanks for your rapid reply.

There are no other ports apart from the plugs at either end of the tank. Which I'm not sure are for this purpose.

I'm considering just blanking off the regulator outlet and using one of the ports on the new pressure switch instead. Is this safe?

Dean

 

[Robotstar5]

There are no other ports apart from the plugs at either end of the tank. Which I'm not sure are for this purpose.

You can use the cylinder end plugs, just need a reducer to match your new parts, I used one to give me a hi-flow unregulated outlet.

 

[rtbcomp]

Using the end plugs is a much better idea than using the spare port on the pressure switch. The latter is only 1/4 BSP whereas the end plugs are more likely 1/2".

Put a ball valve on the regulated output, you may just need it, you never know.

 

[Dean1983]

I have decided to do a combination of your suggestions.

I will put a ball valve on the faulty regulator output (it doesn't open fully that's why it's faulty) and use it to discharge my tank after use.

I will then install a 3 port pressure switch with a tank gauge, a regulator with output gauge and safety valve on it.

I will then also be adding a 1/2 fitting to the end of the tank like Robotstar5 has for anything that doesn't need to be regulated.

Thanks for your advice. You've solved my dilemma in just a few hours!

 

[rtbcomp]

Good.

If you want to discharge the tank after use you're better off using the drain valve on the bottom. This will expel any condensed water.

Let us know how you get on.

 

[Dean1983]

Right,

The postman bought me my parts and all installed and working great.

I do have one question, the small bleed pipe from the bottom of the pressure switch to the compressor leaks at both connections when I disconnect either end and blow down the pipe.

One is a push fit and the other end is a compression fit. It's the bit labelled 6.5mm in this photo.



Is this supposed to leak air?

Also my pump states 9.0 cfm and my tank is 50 litres. How long should this take to fill? I timed 3min 20secs from 90 to 120 psi. Is this right? It's an oil free compressor and I've cleaned the reed valve which was dirty.

Thanks in advance.

Dean

 

[rtbcomp]

That little valve should only let air out when the pressure switch opens, this gives the characteristic hiss when the motor stops. If you ever switch off at the mains with the pump running you must then switch off at the pressure switch to let the air out of the pipe between the pump and the tank. If you don't the motor will try to start under load and could be damaged.

If you disconnect the pipe you will get air coming out if the pump is running. If you switch off at the pressure switch (or disconnect the pipe) and and you get a stream of air then the non-return valve at the tank is faulty.

My SIP 3hp 13 cfm displacement takes 5 mins 12 sec to fill 217 litres from 0 to 80 psi. Try timing 0 to 80 on yours.

 

[Dean1983]

Hi and thanks.

It doesn't leak continuously when pump is stopped. It just has the brief hiss you mentioned.

It does pump air if I disconnect it when running.

I think all is working fine, it's just a little slow to charge. Not timed 0 - 80 but I will. I think it's just a worn piston or cylinder. Are they any quick fixes for this? As I've said, I've cleaned the reed valve and head which was encrusted with soot like substance.

And can I just ask how you know so much about these things?

Dean

 

[rtbcomp]

Learnt most of it from here http://www.mig-welding.co.uk/forum/forums/compressors-and-air-tools.40/ And taking things to bits to see how they work

If it's oil-less then it probably won't have a conventional cylinder/piston arrangement, Google "how do oil less air compressors work"

 

[Dean1983]

Thanks for your help on my compressor. I have another question. Hope you don't mind? I'm sure it used to hiss when it stopped automatically. Now it doesn't appear to hiss when it stops on it's own unless I use the red switch to turn it off at the pressure switch.

Update:

After a little testing I can see that if I shut the pressure off on the pressure switch quickly it hisses as it should. If I operate the switch slowly it doesn't hiss. I'm just thinking that this thing is so inefficient at charging that it doesn't have much air in the charge pipe to bleed off?

 

[brightspark]

Thanks for your help on my compressor. I have another question. Hope you don't mind? I'm sure it used to hiss when it stopped automatically. Now it doesn't appear to hiss when it stops on it's own unless I use the red switch to turn it off at the pressure switch.

Update:

After a little testing I can see that if I shut the pressure off on the pressure switch quickly it hisses as it should. If I operate the switch slowly it doesn't hiss. I'm just thinking that this thing is so inefficient at charging that it doesn't have much air in the charge pipe to bleed off?

will probably be slight loss of air back through the worn valves and rings

 

[rtbcomp]

When you operate the switch slowly you may be letting the air out gradually. The switch mechanism uses a toggle action which should operate the switch (and the valve) quickly.

Try letting it get up to pressure and when it stops, quickly operate the red button and see if you get the hiss. If you do then there is still air in the delivery pipe (the pipe that runs fromm the pump to the tank) if it doesn't hiss then it sounds like the air has leaked away.

Repeat the experiment but wait about 30 secs before operating the switch.

Be careful not to let the pump restart jsut in case there is some pressure left in the delivery pipe.

As BS says, this could be a worn outlet valve on the pump.

It may be worthwhile blathering some soapy solution around the joints in the pipes, keep it away from the electrics though.

 

[Dean1983]

Test results.

Hitting switch immediately after pump stops. Hiss from pressure switch.

Waiting 30secs before hitting switch results in nothin. What I did notice is a little hiss around 15 secs in that sounded like a release.

This is a new pressure switch, is it faulty or just slow to release the excess air?

Dean

 

[rtbcomp]

Try some soap solution around the bottom of the pressure switch, where the unloader valve sits, if you get bubbles with the switch in the "on" position either the valve or the union is leaking.

 

[Bill Edwards]

It sounds to me like your switch is working, but I can't say whether it's OK.
I believe they should release immediately - most of the ones I can recall do - but I'm open to new ones!
I do know an old compressor that does it slowly like yours is, I tend to think it is faulty rather than designed that way.

 

[Dean1983]

Will a replacement pressure switch fix this? I could ask the eBay seller to replace as faulty?

Thanks

Dean

 

[Bill Edwards]

I think so.