Using a Piston Pump for Air delivery.

[BaboonScience]

Responding to some questions about my air delivery system.
I currently use a piston pump to charge up a high pressure cylinder to about 80 PSI.
The pump and regulator.
The pump is from a small portable system (Emglo AM782HC4V Air Mate Compressor ) and can deliver up to 4 CFM at 90 PSI. I picked it up used at a flea market for $35 complete.
I have set the pump cut in pressure as low as possible (about 35 PSI) and the cut out pressure at just under 80 PSI.

The pressure tank.

Although the system comes with a pair of pressure tanks, they are quite small and the cycle time would be reduced. I had a larger tank, 60 gallon (http://www.pneumaticdepot.com/pdf/manch ... ank/302473), that has a mount for a much larger pump. These can be had used all over the place and for a fraction of the new price.
I removed the regulator and pump from the Air Mate system and mounted them on the larger tank. Once plumbed, it takes the pump about 1.5 minutes to pump from cut in to cut out. The pressure valve was plumped directly into the air in to the large tank.

Low pressure air supply.
I plumped a ball valve directly into the air out from the large tank. I also plumbed the pressure guage from the Air Mate to this point. I placed a reducer after the ball valve that takes the line from 3/4 inch to 1/4 inch. The 1/4 inch supply line is poly (refrigerator ice maker supply line) and delivers high pressure air to the air dryer and low pressure regulator. You can get these at most hardware stores and they are not expensive. The air dryer removes residual oil and condensed water from the air supply. The regulator will regulate air down to 5/10 psi. I added a low pressure gauge here to monitor the air delivery. Low pressure supply can be teed and distributed the same as any other low pressure supply.

Noise
Yes, uninsulated these units are loud. I placed the assembled unit in a location outside of my lab, away from the house a bit. I also built a box around the compressor that does an amazing job. I built the box from scrap plywood and furring strips and built it large enough to place insulation on the inside. If you do this part, remember to place the insulation so that the sound absorbing (soft) part is facing toward the pump. You will also need to place screen of some sort on the inside of the insulation so that the insulation is not drawn into the compressor fan. I am sure that there is a better way to soundproof but this is good enough that the noise is much less than a diaphragm pump.

Notes:
I also placed a flexible extension and an air filter on the pump intake. You can use your imagination when doing this.
You will need to keep the pump lubricated. This requires 30 weight standard motor oil and one quart will last forever at the cycle rate of 4 min/hour.
I built this from surplus and used parts in order to see if it would work. It exceeds my expectations but does require a DIY mentality.

I will try to get pictures but you know how good I am with the camera.
Have fun.
John

[rsman]

a pressure sensor on the low side, and high side will allow it to run until well below 35psi, you can even go lower than your low pressure regulator if you dont need the pressure your low pressure regulator will allow, larger tanks and a timer will allow it to run early and late so its not running over night. a nichrome wire in a piece of pvc inline on the low side will allow you to easily heat the air taking the edge off from the outside temperatures and the compression.

[BaboonScience]

Great ideas.
Funny thing is , I had not even thought of the cooling effect of air decompression. That low pressure valve runs pretty cold.
Tho do you power the nicrome wire?
I have melted my share of PVC.
Thanks
John

[Chuck]

Hi Guys,
Great ideas and great setup BaboonScience

I heard that the cheapest and quieter air compressor available come from a refrigerator or a congelator. It can be salvaged from a damaged unit or a free unit on kijiji and these things are made to last. The max pressure is about 30 or 35 PSI and I have no idea of the CFM output, but I was thinking of adding more than one on the same tank if needed.

I didn't test any of these yet but I hope that this could help you guys

Chuck

[BaboonScience]

Another good idea. I think that the max pressure is considerably higher than 35 psi but these units work very well as vacuum pumps also. These are rotary pumps but that is another form of piston pump design, I believe.
Things to consider would be...
What lubricant and how do you cycle it.
You will need to bleed the remaining freon from the residual oil in the pump.
The CFM that you mentioned in your post.
Amperage draw vs CFM and pressure compared to a conventional piston pressure pump.

I have a couple of rotary refrigeration pumps sitting in the shop. After your post, I guess that I will have to give one a try to see how effective they are.
Thanks
John

[rsman]

normal refirig pumps are not designed to work with a 100% duty cycle, and are oiled by the oil in the refrigerant, once you get around that and its probably not a bad idea

a bolt and a few nuts/washers will hold and supply power to the nicrome wire without touching the pvc if you get your nicrome out of an old hair drier then use some of that metalic cardboard to create a form to increase the length of nicrome without increasing the length of pvc. I just have a resistor inline to turn it down a notch so its not running at full speed and it stays on 24/7 i dont really know the wattage draw but it cant be much

[BaboonScience]

Thanks rsman!
The fridge pump would seem to work if you could keep the cycle relatively short and build pressure to a tank. Then it would have a chance to cool between cycles. They probably don't labor too hard until the back pressure starts to build. The oil cycling is another story. Wonder if you could place a larger tube on the output (high pressure side to collect the oil, then it would drain back when the pump stops.

The hair dryer idea is one that I had not thought of. Unfortunately, we just tossed a dead hair dryer. Should have known that the one time that I actually get rid of something... ... I never get rid of anything, I am told.

John

[rsman]

[BaboonScience]

Good point. It seems that refrigeration pumps are specifically designed to operate in a closed system where other compressors are designed to operate in an open system.
The pressures that I am talking about are significantly lower than the maximum operating pressures of the standard piston pump. Used pumps and even new pumps can be had for very low prices in most places. I believe that I could have built my current system using new parts for under $500 if I had shopped around. As it stands, the price was well under $100. The amperage draw is just slightly higher than my best diaphragm pump and it is only operating part time while the diaphragm pump was operating 24/7.

It would, however, be an interesting exercise to find a way to efficiently utilize a refrigeration pump.
John