Another compressor unloader question.

[Hchrist]

I have a Jenny single stage GU pump that I converted to electric from a gasoline engine. When doing so I did some research regarding the unloader. The gas was set up as continuous run and my electric is set up as start/stop. I forget where I got the information but it led me to believe that I didn't need an unloader on the pressure switch. I recall reading that the unloaders that are built into the heads of these pumps relieve the pressure when the pumps shuts off so a separate unloader on the pressure switch isn't required. The compressor ran fine. It always started without issue etc. Recently I had a motor issue which I'm ironing out but, while waiting for a couple of parts, I had this unloader thing pop into my mind again. I've seen many units pictured without an unloader on the pressure switch so I'm thinking I'm OK with my current set up but wanted to see if anyone here has experience with such things. My pump is no longer mounted to a tank. It sits on the floor and is plumbed to a tank that's about 8' above it.
Thanks

Galaxy S4, Slimkat
If I wasn't married I'd quit fishing

 

[The Cobbler]

gasoline engine compressors use pilot unloader valves

 

[sberry]

On a gas you may not have the same unloader, it may use a pilot valve which opens a valve on the head and ideally a throttle control hooked to it. It essentially acts as a pressure switch, idles the unit down and opens the heads. An electric can simply unload the head pressure after the unit stops, dump it all North of the check valve so it starts easy. Turn it off and on with a pressure switch. There are a couple types of unloaders, I don't remember it all at the moment.

 

[BillK]

The compressor ran fine. It always started without issue etc.

I think you answered your own question right there. If it ain't broke, don't fix it

 

[The Cobbler]

pilot unloaders open when tank pressure is reached and via a throttle cable they idle the engine down. when the tank pressure lowers the valve closes, throttles the engine back up and tank pressure builds .
the compressor pump is running continuous while the engine is running

 

[RocketScott]

Something needs to unload the head.

What unloaded it before? (when it was gas)

What is unloading it now?

 

[The Cobbler]

OK, me bad, I was multi tasking and read the post wrong.
I realize now OP has converted from gas to electric.
so
you need a pressure switch with an unloader port , that then would get plumbed in to the pressure side of the pump ( between the pump & tank check valve) sometimes there's a port on the head
when the pressure switch shuts off, the unloader port opens and bleeds the pressurized air in the head and pipe to the check valve. by doing that the compressor doesn't start against pressure, rather it starts against atmosphere pressure

 

[Hchrist]

I know I'm missing something. Either I don't understand why it DOES work (start) OK (and has been doing so since I converted it) or I don't understand why it shouldn't work. I'm thinking that the head unloader valves unload the pressure inside the cylinder heads so that the pump does indeed see atmospheric pressure when starting.
I'm not trying to convince myself that's its OK without a pressure switch mounted unloader valve but it has been working for a few years, other than some substantial repairs due to wear, AND that I've seen photos of it there compressors without pressure switch mounted unloader valves.
BTW - I don't have any tank check valve installed.
Thanks

Galaxy S4, Slimkat
If I wasn't married I'd quit fishing

 

[The Cobbler]

if you don't have a tank check valve I would think you would hear & lose air pressure as soon as the compressor shut off. it would back feed.
you may not have any issues without the unloader but if there was one installed it would make for easier start ups . there could be a small unnoticed air leak somewhere that is acting as an unloader

 

[goodwrench]

it might have an unloader that works off rpm. does it have a line running from the head down to the side of the pump where the crank would be? some had a centrifugal unloader that ran off the crankshaft that when the rpms dropped would unload the head.

 

[The Tool Tyrant]

I know I'm missing something. Either I don't understand why it DOES work (start) OK (and has been doing so since I converted it) or I don't understand why it shouldn't work. I'm thinking that the head unloader valves unload the pressure inside the cylinder heads so that the pump does indeed see atmospheric pressure when starting.
I'm not trying to convince myself that's its OK without a pressure switch mounted unloader valve but it has been working for a few years, other than some substantial repairs due to wear, AND that I've seen photos of it there compressors without pressure switch mounted unloader valves.
BTW - I don't have any tank check valve installed.
Thanks

Galaxy S4, Slimkat
If I wasn't married I'd quit fishing

You need both an unloader valve AND a tank check valve. If not, your poor motor is trying to start with a huge pressure load against the pump pistons!
Sure, it may be working as is, but you're greatly reducing the lifespan of your motor. It's like trying to take off from a dead stop in 4th gear with a manual transmission.

The Jenny/ Emglo GU pumps use a pressure switch style unloader in start/stop function.

 

[Hchrist]

Got it now. Thanks

Galaxy S4, Slimkat
If I wasn't married I'd quit fishing