Up grading an older air compressor


Old 06-29-04, 11:17 PM
Visiting Guest
Posts: n/a
Up grading an older air compressor

I have my fathers older oil air compressor and would like to update it. I have no idea what brand of compressor it is, I've looked but to no avail.

It has 2 air tanks and the compressor has 2 pistons, but I'm not sure if it's a two stage or a single stage. Which I need to know because I need to add a pressure switch. The original air compressor was a gas driven machine, but my dad changed it to electric 240v about 8 years ago. The original compressor was and still is set up with a pressure switch which does not shut the motor off but just disengages the compressor, which makes sense for a gas unit but not electric.

So I am wanting to add a pressure switch to shut off the electric motor. The current pressure gauge only goes to 100 psi. I have looked at this switch but I'm sure it's not rated low enough. http://amos.shop.com/amos/cc/main/ca...Air_Compressor I'm going to use a small nailer and maybe later on use it to spray varnish.

Any help or thoughts are appreciated
Sponsored Links
Old 06-30-04, 06:05 AM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 9,779

You don't say how big the motor is but as long as the switch is rated for the motor's amperage it would work.

<img src="http://altura.speedera.net/ccimg.catalogcity.com/210000/211300/211368/products/5631719.jpg">
Image credit: shop.com

Single or two stage doesn't matter.
You would need to remove the electric clutch and replace it with a fixed pulley of the same size.
You then would have to make sure there is a check valve on the discharge line from the compressor at the tank.
The small bleed valve that you can see on the left side of the pressure switch has to be then piped into the discharge line so as to be able to bleed the pressure from the compressor head before it restarts.

The normal cut out pressure should be 100 psi so the guage should read up to about 150 psi.
Old 06-30-04, 06:55 PM
Visiting Guest
Posts: n/a
The motor is 2 hp.

Here is a picture of the compressor.

There is no electric clutch on this unit. My thinking is the two lines on top if the cylinders disengages the compressor some how. Anyway I thought I would just leave that stuff alone and just add the pressure switch making sure that the old shut off is set higher than the new pressure switch.

Old 06-30-04, 08:15 PM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 9,779
It's a two cylinder, single stage pump.

Boy, it's a shame to remove the governor set-up.
If you don't know the principal of operation, once the pressure of the tank matches the spring pressure of the governor near the bottom of the compressor a valve opens and sends air to small pistons on the top of the head and pushes the suction valves open, causing the pump to stop compressing air.
What you need to do is either remove all this piping and cap it off or if adjustable set the cut out pressure at about 125 psi.
Then you have to install a check valve where the discharge line from the compressor enters the tank.
Following so far?
Next you need to install a tee in the discharge line and connect a 1/4" line from this tee to the auxiliary connection on the pressure switch. The pressure switch main connection then goes to a tank fitting.
Then set the pressure switch at 100 psi to be lower than the governor setting.

You must connect this small line because when the motor shuts off there will be tank pressure pushing against the pistons on the pump. The motor will not restart because it won't have the power and will trip the breaker or just sit there and hum.
All compressors have this or something similar.

I don't suppose you still have the gas engine?
If you look at the size of the pulley the pump will not be turning very fast, meaning it is delivering only a small fraction of the air it is capable of.
It would have had at least a 5 hp gas engine.

Honesly, I don't know how much air you use but if installing a switch is too much trouble a better project IMO would be to see if you can locate a gas engine and restore it to its original purpose.
Strip it apart, clean it really good and apply a coat of paint and it will look like new.
This is the kind of project I like doing.

What rpm is the electric motor?

Need more just ask.

<img src="http://www.budgetlighting.com/shop-tools/compressor3.gif">
Old 07-02-04, 07:24 PM
Visiting Guest
Posts: n/a
I still have the gas engine.

Last edited by sborder; 07-02-04 at 10:46 PM.
Old 07-09-04, 10:52 AM
Visiting Guest
Posts: n/a
Was there some reason you wanted to know if I still had the gas engine?
Because I do have it.

Old 07-09-04, 09:46 PM
GregH's Avatar
Super Moderator
Join Date: Jan 2001
Location: Manitoba
Posts: 9,779
Talking Thanks for waking me up.


I'm really not sure what your air needs are but an engine driven compressor has way more value than an electric one.
Considering that you will have to modify it to install a pressure switch set-up installing the gas engine and returning it to it's original condition would make more sense.
Your unit could likely handle up to a 5 hp electric motor so the 2 hp that is on it now only uses a fraction of it's capacity.

For use on a small nailer or sprayer you likely could buy a small compressor for almost the same money as the parts to convert your existing unit.

I'm not sure if you are into restoring things but a bit of scrubbing and a couple of cans of spray paint would make that unit look like new.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Display Modes