I milk a cow with a pulsating milk machine that uses a fair amount of lpm/cfm to operate the milker. My vacuum system has a 5 cfm vacuum pump attached to some brass fittings then to a pipeline made from PVC. A simple regulator is connected to the brass fittings. And we have a large vacuum tank connected to the PVC line.

When we connect the 1/2 inch vacuum line to the system and turn it on, the vacuum pump can keep the suction going. The gauges read about 12 to 13 inches of vacuum (units are inches of mercury), which is what the milk machine needs to keep suction. That's about -45 kPa.

We had an accident when we first started using the machine. We apparently sucked in a large amount of water during cleaning, and sent a good liter of water into the system. The pump is a rotary vane pump that has a sight glass for the oil. Any liquid water in the system quickly ruins the pump. Of course, the pump started to sound different, and we turned off the pump to protect it. Our PVC lines had places to unscrew and drain the water out.

But for next time, I thought that we should use a water separator, one designed for air compressors, as I own one. I figured that with so much cfm being used by the vacuum pump during normal operation, that the lines would mimic an air compressor volume of air flow. I think water separators use centrifugal force and baffles and a filter, probably fine for my application.

My main concern is cost. I could get a really expensive cast iron pump made for huge dairy operations, or switch to an oilless vacuum pump, and get an inline water separator designed for vacuum systems. But since accidentally ingesting massive amounts of water is still bad for all sorts of reasons, I will change procedures to stop sucking in water.

My question is whether occasionally ingesting water will be solved by a centrifugal filter/water separator designed for air compressors, perhaps a few teaspoons per milking.

  • 2
    Think most air compressor water separators/filters are made to remove moisture from the air, not the amount from sucking in water.
    – crip659
    Commented Jun 13, 2022 at 18:41
  • 1
    Not knowing what the flow velocity might be, nor to what degree the water might be converted to mist or vapor, but.. if you plumbed it to flow through a (relatively) large-diameter section of pipe to slow the velocity, and also used a tee fitting to attach a trap (a tank or even just a stub of pipe hanging downward), gravity might cause a large percentage of the accidental water to be captured in the trap. Then a separator could focus on removing whatever mist or droplets sneak past the bulk trap.
    – Greg Hill
    Commented Jun 14, 2022 at 0:19
  • I had two traps installed in the pipeline at the low points near inlet and the pump. In the aftermath of our water incident, we emptied both traps and the each had a small amount of water. They are just as @GregHill described, but obviously failed to prevent large amounts of water being drawn into the pump's oil and shutting it down. When we drained the pump, it was a half-liter of water along with the oil. The pipeline is 1 1/4 inch pipe. The largest percentage of water was ingested by the pump.
    – uruiamme
    Commented Jun 15, 2022 at 2:05

2 Answers 2


You would put it in with the flow to the pump.

and yes it would work,

I would get one that you can install electrodes for a water alarm or a clear bowl and a through beam sensor that would shut the pump down.

vacuum works the same as pressure in your case ball park ~7 pounds as 1 atmosphere is 14.7 pounds but the flow is towards the pump.

What you do need is one made for a high flow as restrictions in vacuum lines limit the flow so a larger area won’t throttle your vacuum, I probably would get a chambered separator not one with the sintered bronze as that may limit your flow. You could make one quite easily with a large mouth 1 gallon jar and 2 bulkhead fittings on the lid. Have the milk / water side longer than the pump side the moisture enters and falls to the bottom air exits the top, add a plate between them and you have a chambered separator that you can unscrew and dump/ clean.

  • Except that many structures which can withstand pressure, cannot withstand vacuum. youtube.com/watch?v=UpWeU2fvFGs Commented Jun 13, 2022 at 23:32
  • 2
    My father in law used an old pressure tank about 10 gal with a drain on the bottom. He sucked air out of the top (to the pump) and let it in from the milkers near the bottom. After each milking session he opened the drain valve until the next milling time. It was still working fine many years later when he retired.
    – Gil
    Commented Jun 14, 2022 at 0:36
  • @ Harper a jar can handle 14” of Hg come on it would probably handle close to 25 but then the lid would buckle.
    – Ed Beal
    Commented Jun 14, 2022 at 3:35
  • I guess many on this site have never canned there own veggies or meat. The canning process creates a vacuum in the jar, notice how the lids are pulled down? This is a vacuum not a positive pressure!!! Many internet mnions follow huge lack of knowledge.
    – Ed Beal
    Commented Jun 14, 2022 at 17:26

To prevent the accident happening agin install a water pump.

Here is the sketch


You open the valve and start the water pump. Let it run till not water is comming out.

Turn it off and close the valve.

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