Snap on air compressor leak

[Snapon1]

I recently purchased a used Snap on 40 gallon horizontal 5hp air comoressor model #: bra5140h. Well the problem I'm having is that once the air compressor airs up, it will cut out at 144 psi and then I can hear it bleed off the air for a few seconds and stop. Then I will notice that the guage will slowly start to drop, within a minute or so it will be down to 124-128 psi and will stay right at that for days or even a week, pretty much until I drain it. I've tried spraying down all the connections with soapy water and as far as I can tell I can't find anything. Anyone have any suggestions on what to check? I'm wondering if its something that would only leak at higher psi but then not leak at all at a lower psi.

 

[TTLLOGIC]

The air is cooling down. Air expands when heated and contracts when cooled.

 

[Snapon1]

The air is cooling down. Air expands when heated and contracts when cooled.

Okay, so once the compressor shuts off the air starts to cool down causing the pressure drop? And is that a normal amount of pressure drop after shutting off?

 

[TTLLOGIC]

Yes, with that small of volume of reciver a 16 psi pressure drop after the air returns to ambient temp sounds normal to me.

 

[shop guy]

Okay, so once the compressor shuts off the air starts to cool down causing the pressure drop? And is that a normal amount of pressure drop after shutting off?

If it holds pressure for days/week like you say once it levels out then that's all that matters. If there was an actual air leak it would find it's way out no matter what, so I wouldn't worry about it.

One of my cheap small compressors has a leak at the outlet and if I leave air inside it'll be gone after a day so if you can go a week without air loss you know you're good.

 

[TTLLOGIC]

Using ideal Gas Law calculation. (Pf=Pi*Tf/Ti where T and P are absolute temperature and absolute pressure. ) For example:

Assuming 150 degF air temp after pump. With a 70 degF ambient temp. and 144 psi final pressure. The pressure after returning to ambient should be around 123 PSI.

 

[Snapon1]

Good to know. Thanks for the help! Since the air compressor turns on quite frequently when I'm using it I thought it was due to a leak causing the pressure to drop to where it was close to the cut in. For example, lets say the pressure drops to 124 psi right after filling up the tank and I use an air tool for 20-40 seconds the motor will kick back on to air up. To me it just seems like the motor is working a lot and I want to make sure it doesn't overheat or damage it. Do I just need to get a bigger capacity or adjust the cut in or cut out settings?

 

[alexb2000]

Good to know. Thanks for the help! Since the air compressor turns on quite frequently when I'm using it I thought it was due to a leak causing the pressure to drop to where it was close to the cut in. For example, lets say the pressure drops to 124 psi right after filling up the tank and I use an air tool for 20-40 seconds the motor will kick back on to air up. To me it just seems like the motor is working a lot and I want to make sure it doesn't overheat or damage it. Do I just need to get a bigger capacity or adjust the cut in or cut out settings?

So you are saying that using a typical air tool i.e.. drill for 20-40 seconds it kicks back on? That doesn't sound right with that size compressor. What pressure is it kicking on at?

 

[The Tool Tyrant]

SO1, two things I recommend you do...

First, locate a larger (80 gal+) stand alone receiver that you can plumb into the system, this will drastically cut down on cycling, which saves the motor. Another drawback to a small receiver is it gets hot as it absorbs heat from the compressed air, which attributes to water vapor not condensing which is why you would notice water vapor at the end point of use. (Not good on air tools)

Second, Install a belt guard mounted aftercooler, which will do two things for you, first, it drops the compressed air temperature, which would allow more 'useable' air into the receiver before it reaches cut-out pressure. Next, it turns the hot 'water vapor' into droplets, which can then run to the bottom of the receiver to be removed when you open the condensate drain.

 

[Hpozzuoli]

Using ideal Gas Law calculation. (Pf=Pi*Tf/Ti where T and P are absolute temperature and absolute pressure. ) For example:

Assuming 150 degF air temp after pump. With a 70 degF ambient temp. and 144 psi final pressure. The pressure after returning to ambient should be around 123 PSI.

Now that was cool

 

[TTLLOGIC]

SO1, two things I recommend you do...

First, locate a larger (80 gal+) stand alone receiver that you can plumb into the system, this will drastically cut down on cycling, which saves the motor. Another drawback to a small receiver is it gets hot as it absorbs heat from the compressed air, which attributes to water vapor not condensing which is why you would notice water vapor at the end point of use. (Not good on air tools)

Second, Install a belt guard mounted aftercooler, which will do two things for you, first, it drops the compressed air temperature, which would allow more 'useable' air into the receiver before it reaches cut-out pressure. Next, it turns the hot 'water vapor' into droplets, which can then run to the bottom of the receiver to be removed when you open the condensate drain.

I agree to most of this with the exception of just getting an arbitrary volume receiver. You need to take into consideration other factors before doing so. Such as pump flow at working pressure and pump/motor duty cycle. Adding such a large additional volume will greatly extend pump up times. This could cause you to exceed the duty cycle ratings of your pump/motor. Thus significantly shortening the service life of them.

 

[Snapon1]

So you are saying that using a typical air tool i.e.. drill for 20-40 seconds it kicks back on? That doesn't sound right with that size compressor. What pressure is it kicking on at?

According to the guage the air compressor cuts in at 112 psi. If the compressor cuts out at 144 psi and drops to 124 psi that only gives me about 12 psi to work with until motor cuts in again.

 

[Snapon1]

I agree to most of this with the exception of just getting an arbitrary volume receiver. You need to take into consideration other factors before doing so. Such as pump flow at working pressure and pump/motor duty cycle. Adding such a large additional volume will greatly extend pump up times. This could cause you to exceed the duty cycle ratings of your pump/motor. Thus significantly shortening the service life of them.

Very good information to consider. I might just look into getting a bigger air compressor with motor and pump built in so I know it's rated for it and don't have to deal with anything going wrong.