Milk Vacuum Pump

The ideal pump has the following parts:


1. The PUMP:

surge pump


What is most important about this piece is that it is vacuum (sucking air in) and NOT a air compressor (pushing air out).

To the right, in the photo, is a yellowish tube that holds oil. (I use a Vacuum Pump Oil from a dairy store. I have re-filled mine once and have not refilled it in 3 years.) Note, many new pumps are oil-less. There are pros and cons to both styles, but don’t let it bother you too much as a factor when purchasing as long as the exhaust is clear/clean.

Our Surge pump is an old model, nearly indestructible. Pump models vary by design/style considerably. The Gast pump is a modern model commonly used on vacuum pumps for milking machines.

SP11 Vacuum Pump Specs:  5.0 CFM – 440 RPM – 12 inch pump pulley – 3.25 inch Motor pulley – 1/2 hp motor – 1 quart oil capacity

I am not a mechanical genius, so can’t tell you what all that (above) means, but I can suggest if you buy a different pump, try to find one with similar specs as the SP11. Our pump works fantastically for our one-cow milking system. Buying anything much smaller would put a strain on the pump and likely shorten the lifespan of the pump/motor.

Vacuum pump oil (currently, 2020, available online through Bob White Co. & Hamby Dairy Supply – Hamby’s is listed under Surge SP11/BB Repair Parts)



“To put oil in pump unscrew muffler pipe from Tee and pour oil in Tee. When full, oil should show 3/8 inch in transparent hose when pump is not running. If oil does not show in hose, add to get proper level – always keep oil showing when pump is not running.” 1c

2. The MOTOR:


Our pump uses a Dayton 1/2 hp motor, a perfect size for this pump. 1/2 hp is a good “minimum” effective size for most pumps, although larger pumps may do better with 3/4 or 1 hp.2b

Beware: Some of the older pumps have this pulley system. (While it makes for a very smooth working unit, it can be dangerous to fingers, etc.)

The pumps originally came with guards. Ours did not have one when we acquired it, so we keep that side towards the wall.

3. Vacuum GAUGE:

3The gauge is very important!! Improper vacuum causes one of two problems:

  1. Low vacuum = pulsator will not function or pulsator will work but the inflations will not have enough vacuum to draw milk out of the teats.
  2. High vacuum = stresses teat ends and can cause permanent callouses which flare open the end of the teat, exposing the udder to bacteria, therefore higher risk of mastitis.

Ideal vacuum is 13.5 Hg (not PSI!)

The amount can be adjusted for extra long distance between pump and machine (if the hose to the machine is really long, like 50 feet, up the pressure to 14 or as needed to get adequate pressure to pump.)

Vacuum levels and vacuum controller – The National Mastitis Council (NMC) recommends an average vacuum in the claw during milking of 10.5 to 12.5″ Hg. This normally indicates that the set or nominal vacuum on the system should be 12.5 to 13.5″ Hg for low lines and bucket milkers and 14 to 15″ Hg for high lines.” from Milking Machines and Milk Quality – OSU Article

4. Vacuum PORTS:


  1. The gold colored port on the left is called a vacuum regulator, it regulates the amount of vacuum, and works by simply twisting up or down to adjust.
  2. The port in the middle/bottom is a on/off valve called a stallcock (the handle to switch on/off is out of view underneath). We always leave ours open and leave our air hose attached, but this port may come in handy if your pump is a great distance away. Then, the on/off switch would be where you attach the air hose rather than right up next to the tank like ours is. The other end of the air hose attaches to your milking machine.
  3. The port on the right attaches to the gauge.
  4. The port to the right/rear connects the air tank to the valves.


5aNote: If you DO NOT have an air reserve tank (the large blue tank on the bottom of the setup), your gauge will likely fluctuate significantly.

The needle should not move at all once all four inflations are on the cow’s teats.

If you do have a tank, and you do have issues holding pressure, look at the bottom of the tank and fill in any holes with silicone or something that will help prevent the tank from leaking.

See resources below (from other ingenious sources) for ideas on how to make your own air tank (aka balance tank) for your pump.

We also have an additional section dedicated to the balance tank/moisture trap with ideas on how to buy or make your own.

Click individual photos for more information:






Using a vehicle as your vacuum pump:

Click on the photo below for details on hooking up to a CAR:


The air tank has an open/close valve (always kept closed, except for cleaning). This valve allows you to clean the tank on the off chance you accidentally suck milk up the lines and all the way back into the tank. Open valve, flush from top end with pressurized air or water, then tip to let drain. The modern Nupulse pump has a large plastic disc on the end of the pump that can be removed, which really makes for easy cleaning!


CaptureThis may seem simple, but for those that do not have electricity in their barn, a plug in can become quite the problem! My dad designed a plug in to the motor that has one line (orange) for the power and another line (black) to a “outdoor” quality on/off switch so all we have to do is flick the switch on and off at the beginning and end of milking.

Be careful to never turn the pump off while the hose is attached to the machine if the machine holds suction. I’ve been told it can make the motor or pump seize. Instead, pull the hose off the machine, then turn off the pump and put the hose away. Return to machine and lift one of the inflations to release vacuum hold in the machine.

Below, watch a friend of ours rebuild his Surge pump

(a different style than ours, but similar concept!)

Want to know what a milk pump sounds like? Click here to watch a short video:


0machineKeep in mind, the second major part to milking a cow is the machine. CLICK HERE for information on working the machine.


9 thoughts on “Milk Vacuum Pump

  1. Tyler Thompson

    I have the same pump that is shown above. Mine runs well but wont hold a vacuum. Any thoughts on what I’m doing wrong or what is wrong with my pump.


    1. Sure, my first guess is to tip the pump to its side or over enough to inspect the pump. Often they are sitting on the ground or near the ground and the bases rust out over time. Check for holes and fill any with silicone or a similar sealant that will stick (duct tape works short term!)

      If that’s not the issue, turn on the pump and listen carefully all over to see if it’s sucking air anywhere.

      Check your regulator (should be able to adjust the vacuum greatly, but they can leak if too loose), check all the stallcocks to make sure they’re closed, except for the one with the air hose to the machine (though, if you close that one, the gauge should read higher).

      If none of that works, as me again and I’ll brainstorm some more ideas. 🙂


  2. Uri d

    Does a fluid catch tank can also act as a balance tank?
    I have a lack of vacuum reserve and also some fluid reach the pump, so I’m considering if adding the catch tank (60 liter) will solve both of the problems.


  3. Joshua M Wagner

    help!!!!!!!!!!!!! how do you flush the vacuum pump out with kerosene if milk has gone through the line into the machine? do you suck the kerosene through the air pump hose and circulate through the machine while leaving the drain open?


    1. They’re probably referring to the air tank – if moisture or milk gets sucked up into that area, it could get wet/stinky. Some are designed to be cleaned out easily, like the Nupulse pump, others aren’t designed to be cleaned very much. My Surge has a small valve at the bottom of the tank that can be opened for cleaning, though I’ve never cleaned it in 10+ years.


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