pressure release

[MJ]

It cuts off at 120psi, but the small pressure sensing valve on the back of the pressure switch immediately opens causing the tank to leak down. The small line coming from the non return valve plugs into the back of the pressure switch. Is this a pressure switch problem, or is the non return valve causing this?

[Mark]

Hi MJ, If I understand correctly the safety valve, item #64 on the parts diagram, is opening at 120lbs and not shutting until the tank is drained. If that is the case you most likely have a bad safety valve, part #881-493 which is available from http://www.ereplacementparts.com. The non-return valve is basically a check valve that prohibits the flow of air from the tank back to the cylinder. I hope this helps! -Mark

[PeterB26]

I am having the same problem with mine. It IS NOT the saftey valve, item #64, though it is acting like one. The offending part is not shown on either the http://ereplacementparts.com parts diagram or the original literature that I still have for my compressor.

It is located at the back of the pressure switch and looks like a skinny brass cylinder. The black tube brings high pressure air over from the non-return valve and enters the back of the pressure switch through this gizmo.

Is it part of the pressure switch assembly or a separate part? I don't know... but it definitely doesn't show up as part of the "tube," Item #52, p/n 881-675

Did you solve this riddle, MJ? Anyone?

Thanks

PeterB26

[Jim]

PeterB26 is correct. The part that is causing the problem is a compressor pressure relief valve. is it sown on the Hitachi web site part breakdown.

I am having the same problem.

[kyle]

That piece you are talking about comes on the new pressure switch however I have the same problem so I replaced the pressure switch and it made no difference at all its still doing the same thing.

[DS]

Well I have the same problem and found the diagram on the Canadian Hitachi site shows the part at the end of the hose but they call it a "joint" well it is more than a joint, it has a hole in it and as soon as the compressor fills it trips something that lets the air out the "joint". I have searched the internet and seen many people with the same problem but no real solutions... ANCHOR!

[PeterB26]

This particular thing (compressor pressure relief valve) is actuated by a small brass plunger within the back of the pressure switch. When it is operating correctly it will give a momentary hiss or spit at the end of the pump-up cycle just as the compressor shuts off. That in turn seems to operate the non-return valve. It also releases the pressure on the compressor pump side of that check valve which is necessary for the compressor to be able to re-start.

I took mine off the back of my pressure switch, (there is a single socket head set screw that holds it in place,) and soaked it for a couple of days in some CRC penetrating oil. Then I put it back on the compressor.

Then I experienced an issue where the compressor wouldn't re-start. It would start from scratch, but after the tanks drained down it wouldn't cycle.

I mistakenly and unnecessarily replaced the capacitors at that point. Still the compressor wouldn't re-start, even if I bled the tank all the way down. But it would start with the tanks partially up to pressure if it sat long enough.

At that stage I was reluctant to throw any more money at this problem without knowing if I was going to get a proper fix, so I bought a new compressor.

Lately I went back to mess with this problem to see if I could identify a solution before trashing the whole machine. That is when I discovered that this relief valve actually releases the pressure on the pump allowing it to re-start. With some further tinkering I discovered the plunger that actuates it inside the back of the pressure switch.

When I removed the "compressor pressure relief valve" this time and manually cycled the spring contact arms inside the pressure switch (the unit was unplugged from the power of course) the brass plunger shot out onto the floor. AH-HA!

I slipped the plunger back into place inside the pressure relief valve and reinstalled the whole thing into the back of the pressure switch.

The first time the compressor pumped up the pressure relief valve did the bleed down thing again, so it seemed like I was back to the original problem. But after two or three cycles it began working properly.

Apparently the pressure relief valve is subject to getting sticky with dirt or some other sort of corrosion or contaminates.

If you are having difficulty with this item, or if your Hitachi compressor is having trouble starting, try the above fix first.

I wish I had known about it. It could have saved me the price of the capacitors and the cost of a new compressor.

Also: it doesn't appear to come apart easily from the tube that runs over to the non-return valve. If you have to get a new compressor pressure relief valve you might want to order a new tube to go with it.

PeterB26

[PeterB26]

This problem is NOT the with the Compressor Pressure Relief Valve where the air is leaking out... it is caused by the non return valve not functioning properly.

The Compressor Pressure relief valve is mechanically actuated by a plunger inside the pressure switch assembly. It is supposed to give a momentary hiss just as the compressor shuts off. If the non-return valve is operating properly this relieves the pressure on the compressor side of that valve so it can re-start without having to work against high pressure.

If the non-return valve isn't working and doesn't stop the back-flow of air from the tank, the tank will continue to empty through the Compressor Pressure Relief Valve until the pressure switch's internal mechanical actuator allows it to close. In other words until the tank pressure is almost all the way down to the point where the pressure switch is about to turn the motor on again.

I suspect a sticky non-return valve may also be the cause of some of the hard-start issues others have experienced. If you are experiencing a hard start, even when the compressor is relatively warm and you ARE NOT USING an extension cord, you can try two things to test it out.

First test: if the compressor actually starts and fills the tank, listen for a momentary hiss just as it shuts off. If that happens the non return valve and the compressor pressure relief valve are doing what they are supposed to do. In that case check your capacitors.

If you get a prolonged hissing and pressure bleed down just when the motor stops the Non Return Valve is stuck. The Compressor Pressure Relief Valve where the air is coming out is NOT the problem, but rather the Non-Return Valve.

If you get no hiss at all either the mechanical actuator inside the pressure switch is not functioning, or the compressor pressure relief valve is not functioning. Either way the compressor won't easily re-start because it has to work against the air pressure in the tank

Second test: If your compressor won't start at all try this approach: try cracking (just crack, don't totally remove) the flare nut on the copper line which is on the inlet side of the non-return valve and let all the back pressure bleed out. If the non-return valve is working, or the unit has been sitting awhile there may not be any pressure there to escape at all. But if the non-return valve is sticky, cracking this fitting open may or may not bleed the entire storage tank. Re-tighten the flare nut when the air stops escaping. If the compressor motor then starts and runs, your problem may lie with the non-return valve and/or the compressor pressure relief valve. Confirm their proper operation by listening for the short hiss as the motor shuts off.


This is an update to a post I wrote yesterday on how I fixed my problem. It didn't dawn on me until after I submitted that post that the problem has to be in the Non-Return Valve, not the Compressor Pressure Relief Valve.

I hope this information is helpful to someone.

PeterB26

[PeterB26]

If you have the problem where the machine pumps up to pressure, then bleeds back down again through the valve on the back of the pressure switch and recycles;

OR if your compressor pumps up from empty to pressure, but then won't restart;

check your non-return valve first.

For the older compressors this is part number 881-581 and can be properly identified by the following configuration:


Outlet: (tank side) FEMALE PIPE THREAD !!
Inlet: (compressor side) Male flare fitting
Pressure Switch tube : Male compression fitting

For newer compressors this is pat number 160-591 and is identified as follows;

Outlet (tank side) MALE PIPE THREAD !!
Inlet (compressor side) male flare fitting
Pressure switch tube: male compression fitting

I had the older one. I ordered a replacement valve, but in the meantime I took the cover off the broken one. I don't know if this is possible with the newer style valve. I discovered that the rubber stopper within was swollen and didn't move freely in the valve housing.

The problem is that the rubber stopper absorbs moisture and/or any solvents in the compressed air if the machine is left without draining for long periods of time. ( I am bad about doing this as I am usually working in a finished house and there is no simple clean way to drain the compressor without dragging it outside. So I tend to ignore that recommended procedure until the end of the job. My bad.)

I fixed mine by popping the top off the non-return valve; wiping the rubber stopper down with a bit of mild solvent (paint thinner or alcohol will do) and then placing it on a sunny and warm window sill for two days while I awaited the arrival of the new part.

The swollen stopper out-gassed all the absorbed moisture and returned to its original size. After re-installing it the compressor works fine.

A thread further down suggests sanding the diameter of the stopper down. That would work too and I see very little downside to doing so. Just be careful and clean the stopper well before reinstalling so as not to introduce any tiny rubber particles in to the air stream and your tools.

I stashed the new part in my spares bin (Along with the two new but totally unnecessary capacitors) for emergency use in the future.

Bottom line is that if you have this problem you can probably fix it yourself faster than you can source the replacement parts. AND you can probably avoid it in the future by being good about draining the tanks nightly.

I hope this saves some people the expensive "learning curve" I had to go through!

PeterB26

[PeteT]

PeteB26 is 100% correct. After suffering with the bleed down problem since I owned the EC 12 I found this web site and followed the directions given and fixed the problem immediately. I had some problem identifying the non-return valve as it is not shown on the diagram and I originally thought it was the fitting at the end of the flex hose by the switch box (which does have a little brass plunger in it, so if you detach it be sure to put that back in place). It is actually the fitting at the other end of the flex hose attached to the tanks. After getting this figured out, I removed the valve and found it full of rusty water, which I dried up and then lubed the housing and the rubber stopper that seats to block the air flow, and voila! When I re-assembled the thing the compressor worked perfectly. I highly recommend WD-40 for the lube as it is made to specifically get water off things. Hope this helps someone else.