Question about where to plumb unloader valve

[BareBones]

I have a Gardner Denver Compressor Model ACDB9C9A. I believe that I need a pressure switch with an unloader valve because the compressor starts fine but when it tries to start with pressure in the tank/head the electric motor pulley spins and is unable to turn the compressor. I think that's right.

Then if I get a pressure switch with an unloader valve where do I plumb the other end of the unloader valve in? Since there is no provision for it in the head of the compressor.

Thanks,
Bob

 

[trackwelder]

http://www.marcusecompressor.com/ These guys have all kinds of parts, decent prices, and knowledgeable staff.

 

[walrus]

Unloader valve in the pressure switch doesn't sound right to me. You need to unload the pressure on the top of the cylinders. The ones I've worked on just unload into the atmosphere

 

[Charles (in GA)]

Unloader valve in the pressure switch doesn't sound right to me. You need to unload the pressure on the top of the cylinders. The ones I've worked on just unload into the atmosphere

Normally, the pressure switch has a valve mounted on it. When the switch opens, shutting off the motor, it depresses a valve plunger. The valve is usually connected to a tube running to the compressor head, or if not the head, it is connected to a fitting on the side of the check valve that is screwed into the tank. In either case it is effectively plumbed into the same place, as it vents off the pressure on the head and down the pipe to the check valve, when it shuts off.

If you don't have a fitting on the head, follow the large line from the head down to the tank. The fitting where it goes in the tank is a check valve, that retains the pressure in the tank. These usually have a small 1/8" pipe thread port on the side of them, outside of the check valve, and the tube from the pressure switch is connected to this port. Possibly it is there, but plugged off.

If this is a two stage pump, there should be an over pressure relief screwed into the head or plumbing between heads, that provides a safety pop off of the pressure between the large (low pressure) cylinder and the small (high pressure) cylinder. In addition, there should be a pressure relief screwed into the tank, to vent off pressure in the case of the pressure switch sticking and over pressurizing the tank. Both of these pressure relief valves will probably have a small round "key ring" attached to them to allow you to manually open the valve.

Many larger, more expensive, quality compressors, such as the G-D, Quincy, Saylor-Beale, Curtis, will have centrifugal unloaders. These have a housing on the end of the crankcase opposite the pulley, with a centrifugally operated valve inside, with a small tube running to the head or check valve. These stay open at low speed and close when the pump comes up to running speed. When the pump stops turning, the flyweights open a valve and blow off the head pressure. Many of these are connected to tank drain valves that, the pressure the valve blows off, operates another valve that drains water off the tank, momentarily, each time the compressor shuts down.

Charles

Tank check valve with unloader port in the side of it.

https://www.surpluscenter.com/item.asp?UID=2009043019392545&item=4-1769&catname=air

Follow the small copper line that runs from the end of the crankshaft at the red tag, and turns down to the tank. This is a centrifugal unloader, with the valve in the pump end, and the line connecting to the check valve at the tank, where the large line from the head connects.

Note on this one, the centrifugal unloader on the end of the pump housing connects to a fitting on the head on this unit. Note on the top of the interstage heat exchanger/cooler on the right, the interstage pressure relief valve.

 

[Identaltech]

when the unloader valve is in the pressure switch you tee it in between the check valve and the head.
make sure the check valve is working.
that may be your problem.
if no check valve then he unloader valve will bleed untill the tank is empty.
check valve holds the pressure in the tank so the unloader valve relives pressure on the head
good luck
if you want just just frieght it to me and I could find a place for it.

 

[BareBones]

First off thanks for the help. There is a 1/8 hole that's blocked off on the side of the check valve. It's only a single stage but with 2 cylinders. Opposite the crankcase pulley there is no provision for a a fitting just a plate that allows access to the crank. So I think I will look into plumbing it into the side of the check valve.

I emailed Marcuse Compressors to see if they have a pressure switch that they reccomend. I will post some pics when I get home of the beast. The weight of this alone dictated that I take the tank apart from the compressor and the motor and use an engine lift to unload it.

Bob

 

[3/8"indestro]

if its the VP10 pump,I don't think that one has a centrifugal unloader.

http://www.gardnerdenverproducts.com/assets/0/180/132/188/f2779e8e-3712-4015-b9a9-c79f4fb91d21.pdf

as Charles has mentioned,you will need to run a line from the check valve to the pressure switch.

here's an example:



this one has the unloader plug form the head,and is run from the check valve to pressure switch.



the pump on the far right has the line from the head to the check valve.



the one that has tape on it is the centrifugal unloader:

 

[BareBones]

Here are the pictures I promised. It's not the VP10 compressor you mentioned it is much older.

Here is the whole thing.
<a href="http://s68.photobucket.com/albums/i32/choppeddodge/?action=view&current=new010.jpg" target="_blank"><img src="http://i68.photobucket.com/albums/i32/choppeddodge/new010.jpg" border="0" alt="Photobucket"></a>

Here is where I believe I should plumb the unloader valve.
<a href="http://s68.photobucket.com/albums/i32/choppeddodge/?action=view&current=new0072.jpg" target="_blank"><img src="http://i68.photobucket.com/albums/i32/choppeddodge/new0072.jpg" border="0" alt="Photobucket"></a>

Here is the current Furnas pressure switch.
<a href="http://s68.photobucket.com/albums/i32/choppeddodge/?action=view&current=new012-1.jpg" target="_blank"><img src="http://i68.photobucket.com/albums/i32/choppeddodge/new012-1.jpg" border="0" alt="Photobucket"></a>

I am still waiting to hear back from Marcuse compressors that was mentioned earlier in this post. It's been about 2 weeks and I'd like to get this thing up and running. Does anyone have any other reccomendations on where to purchase a pressure switch with unloader valve.

Bob

 

[BareBones]

Ok I have it all wired and plumbed up but I still have a problem I think. When the switch is on and the compressor is running it works fine no leaks. But when I turn the switch off the unloader valve begins releasing air even if I only have 20lbs of pressure in the tank. Is this normal or is something wrong?

I used a Campbell Hausfeld compressor pressure switch model gr0045. Here are some pics.

Thanks,
Bob