Compressor cushion chamber ??

[Indyducati]

I've a question for the compressor experts.

When I look at old compressors, many have a cushion chamber.
I don't see this on new compressors.

I can't find a very good explanation of the cushions purpose.
Are they obsolete ? If nothing else, I think they look cool.
More fins are always better

I've tried to attach a photo to this post. The cushion is the
finned cylinder on the output line of the pump,
before the air goes into the tank.

Thank you,
Steve

 

[zkling]

A cushion chamber is used to dampen out pulsations from the compressor to tank, especially on large bore compressors where one stroke will pump quite a bit of volume into the tank. They are usually used when a larger output compressor is mated to a small-ish tank. It prevents the tank and supply air from pulsating. High pulsations can cause fatigue in certain areas as well as disrupt air supply at source. Say for example when using a spray gun for painting. It would be like holding a garden hose and having someone jump repeatedly on the flowing hose. The stream's impact point would change.

On low RPM compressors like that old Quincy pictured, the frequency of pulsations can be pretty low, so if you took a "sample" of the pulses it would have pretty large peaks and valleys. Newer small compressors have a much higher RPM and thus a much higher pulsation frequency, the higher the frequency closer the supply becomes to being steady state.

Keep in mind Quincy is one of, if not the premier compressor manufacture. They went above and beyond to produce a premium product.

 

[Indyducati]

Thank you zkling ! I appreciate your detailed answer.

My current Quincy is very similar to the one pictured. I'm a Quincy fan, searching a
deal on a bigger QR.

Is this chamber a 'wear' item ? I have not taken mine off. Is there any maintenance to be done ?

Steve

 

[Fixnair]

The purpose for that chamber is to allow the motor to reach full speed before the compressor reaches full load. It is a crude soft start device. Effective though.

 

[zkling]

The purpose for that chamber is to allow the motor to reach full speed before the compressor reaches full load. It is a crude soft start device. Effective though.

I respectfully disagree. That is the purpose of unloader valves. My Quincy compressor has dual hydraulic unloader valves as well as a cushion chamber.

The unloader valves are what allows the pump to spool up before it starts to fight the pressure already residing in the tank. Really useful on compressors with larger bores.

 

[Kevin C]

Curious.... I did some googeling

http://www.pulsco.com/company/library/product%20information%20sheets/800-1007%20GAS%20Dampener.pdf

Kind of looks like a muffler for the outlet.

 

[Fixnair]

I agree with you zkling about the unloaders. But in this case there are no unloaders and as he said many older pumps that were splash lubed had these bottles. The big pulsation bottles used on large recip compressors perform a completely different function. They are as you say to dampen the pulsations. They also install them after a compressor to eliminate air ring as Kevin C says.

 

[zkling]

Fixnair

In this case there are no unloaders because they are usually not needed on small compressors. Unloaders are usually only needed when the pump has a large bore diameter. The larger bore diameter, the larger force is placed on the piston and thus larger holding torque. So by allowing the pump to spool up without pressure (unloaded) it allows the pump to get a running start before it has to work.

Pressure = Force / Area, so for a constant pressure in the compressor ~100psi per stage, as the area increases (bore diameter) so does the force --> torque needed to turn it. Bigger compressor - > bigger pistons, longer stroke = larger force. Once air leaves the head it is trapped by the valve. That unit should have disk valves in it.

Kevin C's paper supports my comment. A muffler is just another type of cushion chamber. It modifies the pulses, pressure waves (what creates noise) and frequency of the pulses coming from the engine. All in effort to create a more pleasing sound while the engine runs.

Most newer compressors of that size have a small check valve between the output of the compressor and the tank to hold back the pressure.

Indy,

You might have a few wear items in the chamber. My quincy setup has a diaphram in the chamber, that is considered a wear item. I don't know if yours has this in there or not. Call up quincy and ask for a PDF manual. They are really helpful on their product support. You can also probably order a soft rebuild kit which would include all common wear items.

 

[930dreamer]

My Quincy 230 has one also, I didn't know what it was until now.

 

[Indyducati]

I've been searching through my Quincy manuals... free downloads from Quincy !
I see a few part numbers for obsolete chambers, nothing more. I'll speak to the
parts people soon and see if anything is still available.

 

[Indyducati]

Folks,

I asked the initial question nearly eleven years ago.
Today, I'm a Quincy cushion chamber collector.
Possibly, the preeminent cushion chamber collector in the world !
I've got two ! Does anyone have a larger collection

Unfortunately, both of mine are the same size. In the first photo, you can see
the original, on my little 1963 A4. Pop can for size reference. The remaining
photos are my other, with all the plugs removed. It's nothing but a cast iron
chamber. There's nothing in it. It weighs six pounds.

The only markings are a 1 and a K stamped in to the top. Both of mine are stamped
the same.

I know there are larger sizes, and cylinder and cube shapes. I've you've got one, I love
to know if you've got any visible markings. I've sent emails to Quincy, without yet a reply.

Steve

 

[finn]

Sounds like a Helmholtz resonator to me.

 

[May Pop]

My old compressor, an hvac unit with 2 Quincy 106s has one for each pump. Built in 1975 it has been my shop air until 3 years ago.
super quiet.