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What kind of pump for central shop coolant distribution system?

exon111

Plastic
Joined
May 15, 2014
Location
CA, USA
We are trying to install a system to pump coolant to all our machines from one central tank of mixed cnc coolant. We used to have a basic cheapo sprinkler pump that would draw coolant from the tank and push it out through a long garden hose that we would drag over to each machine to top it off every day.

Now that we just moved to a bigger shop, we ran ran PEX hoses along the airlines going to each machine so we can run coolant directly to them. Everything is done now but the last part I am stumped on is how to setup the pump that will supply all this. I don't know very much about pumps / plumbing. We bought a 3 HP Dayton turbine pump that will supply about 30 GPM at 60 PSI. The goal is to have it kick on when someone opens a coolant tap down stream, and then turn off when the tap is closed. A basic pressure switch should handle that. The problem is that based on the little I know about home well pump installations, you have to have some sort of pressure tank attached to the pump to keep it from short cycling. Unfortunately, the type of pressure tanks they sell at home depot use butyl rubber bladders, and according to the internet, butyl rubber has very poor resistance to mineral oil, which is the primary ingredient in our CNC coolant.

What would you do in this case? I'm out of ideas and the only companies experienced with pumps in our area only know how to pump water (I spent 2 weeks trying to find one who could sort this ). To recap, the goal is to use a pump to draw coolant from a holding tank and pump it to machines downstream. The pump needs to turn on when someone opens a fill valve on a machine, and shut off when they close the valve. Any suggestions from anyone who has any experience with this would be greatly appreciated!!!
 
For starters your pump probably does not have the correct seal in it to last very long. You should have either a Nitrile or a Viton seal.

You also probably do not want this system to operate at 60psi. You could use a pressure regulator but that still does not solve the pressure tank issue.

I would suggest to backup and not use the turbine pump. Use a pneumatic double diaphragm pump of the appropriate capacity with the proper check valves, housing, and diaphragms that you need for your coolant.

For pressure regulation you will need an air pressure regulator. Just adjust the air pressure to meet the desired coolant supply pressure. When the coolant flow is off at the machines the pump will just sit there with the supply header at set pressure. If a valve is opened the pump will make up for the pressure lose.

No electric pump or controls needed and when the air compressor is off so is the chance of a coolant leak/spill.
 
How tall is the shop ceiling? Put the tank up high. Let gravity be your pump.

Or you could hook it up to shop air.
 
You could set up a pressure tank attached to air supply at 30 or 60psi or whatever, and use a float switch to cycle the pump to keep the tank between about 1/3 and 2/3 full. That gives you a constant pressure, no moving seals/bladders in the tank to wear, and never dead heads the pump.

If you are good with electronics you can bypass the float and just snip the ground lead off of sparkplugs, and attach a wire to the center point down to the desired level. Once the coolant touches the wire it will bring the voltage down, which can be detected by an op amp and used to trigger a flip flop on a contactor (555 timer and small SSR to a contactor makes this very simple).

Absolutely do run a suitably sized pressure relief valve plumbed back into the reservoir.

In an overflow scenario you want to protect your airlines as well. Failure is unlikely, but it doesn't take much coolant to dump in your pneumatics to mess things up. For this I would recommend you use the type of regulator that blows off excess pressure above the setpoint, and put a checkvalve between the source and the regulator. If possible plumb the regulator blowoff to vent over the reservoir.

This way the regulator can bleed off the excess pressure that would otherwise result from the decreasing air volume as the tank is filled. In a situation where the pump fails to shut off, the regulator would likely be overwhelmed by the flow and pressure in the tank would rise to the pressure relief valve setpoint, which would bypass to the reservoir. The check valve would of course protect your air supply.

The easiest way to build this I think would be to use a 20 to 30 gallon tank from a consumer sized air compressor. (Too large of a tank may get too heavy and crush the feet, but would reduce the cycle rate. Your call here). (You can use the compressor head that is probably already mounted on the tank but that's more than I am going to go into right now). The pump outlet and distribution connection would be plumbed together with a T into the tank drain port. Air pressure would be plumbed through a check valve into the regulator, then into the tank through a T where the compressor used to connect. Put the pressure relief valve on the same T as close to the tank as possible. Attach two sparkplugs with added leads through a Y into the tank outlet. They need to be positioned so as to naturally drain condensation back into the tank and not be able to pool up. A water heater tank may also work here, or you could fabricate something yourself. It's up to you to make sure everything you use is sized for the flow and pressure you are dealing with.

I can draw a picture if you are interested in this approach.
 
We have such a system and we use a pneumatic diaphragm pump. The old chugga-chugga two chamber style. You can set the coolant pressure with the air regulator to the pump. Once it reaches max pressure, the pump will quit pumping. No switches, solenoids, or electrics involved.

Here's a 12g/min version of what I'm talking about.

https://www.northerntool.com/shop/t...-2JnKhv0KI2Jr8xZLkxTIGfW37k6QLnRoCyZwQAvD_BwE

Just to be clearer, the pump we actually use is a 1-1/2" outlet and is fed by a 3/4" air line and it supplies about 60 machine tools. 1-1/2" pipe for a header / main and 1/2" drops to each machine with a dead simple ball valve. Very little to break. It's been in use for at least the last 10 years.
 
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How many machines and how many feet of piping ?

Is this a true central coolant system, with no coolant storage
at each machine ?

As far as proper tubing (piping) and sizing, I think you should really
have this designed.

Allot of time will be spent putting it in, you want it to work right, right
out of the box.
 
+1 for the air operated diaphragm pumps. I've used dozens of them in a large industrial facility for solvents and other hazardous materials. Dead simple, little to go wrong, available in a wide variety of materials, no dynamic seals to cause leaks or loss of prime, and no need for any sort of control system beyond a pressure regulator. They're not the best choice for a continuous flow situation due to relatively inefficient operation compared to a centrifugal pump but perfect for your situation.
 
Before rubber bladders a well pump just used a pressure tank. Locate the tank high up, in the rafters if possible, single line down to the pump, from the bottom of the tank. Have a shut off valve on that line and a compressed air fitting or line to the tank.
Shut off tank valve, fill with air to pump pressure. Run the pump then open the valve. The coolant will slowly dissolve the air in the tank into the coolant. So every so often add air with a pressure slightly higher to force liquid out of the tank down into the main lines.
Bill D.
 
Thank you for the replies! After spending half the night looking into this, I stumbled into proportioning pumps. We are just going to use a water power proportioning pump to mix coolant on demand and run it straight to the machines. Much simpler and cheaper than my previous idea with a Venturi feeding a holding tank. This eliminates the venturi, holding tank, tank level sensors, pump, pressure tank etc. Wish I knew about this a month ago before spending so much time trying to design the aforementioned system. At least I can return the pump we bought back to Grainger, no big loss there.
 
Thank you for the replies! After spending half the night looking into this, I stumbled into proportioning pumps. We are just going to use a water power proportioning pump to mix coolant on demand and run it straight to the machines. Much simpler and cheaper than my previous idea with a Venturi feeding a holding tank. This eliminates the venturi, holding tank, tank level sensors, pump, pressure tank etc. Wish I knew about this a month ago before spending so much time trying to design the aforementioned system. At least I can return the pump we bought back to Grainger, no big loss there.

That sounds like a good solution but be aware that the make up coolant concentration level will not be the same as the tank coolant concentration.

This difference is caused by the evaporation water lose vs. the dragout lose of the coolant mixture. Figure about 2-3% less on the proportioning pump then what you want the average coolant concentration to be. This will take several weeks to a month to fully dial in.

Not all proportioning pumps are created equal. The Dosatron is probably one of the better ones in the middle to lower price range.
 








 
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