Friddle’s Vacuum Pump Overhaul

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By Travis Petersen, BOCP, COA

Imagine you have plastic in the oven, about to come out, and you hear the vacuum pump make a horrible noise just before it loses suction. That happened at my lab right in the middle of a bunch of fabrication work. Thankfully, we were able to send the bulk of our work off to our other lab, but we still had to get our pump fixed. Instead of sending it out for repairs, I decided to fix it in-house. Here are the steps I took to fix our Friddle's system with a Gast oil-less vacuum pump that you can use if this should happen to you. Begin by finding your model number on the plaque and starting a list of parts that you will have to order.

Once I hauled the pump out, I saw that it was filthy. It had dust and oil sprayed all over it from the air compressor that sat next to it (Figure 1, left). I recommend cleaning the exterior first so that you don't get dirty while working on it or get exterior dirt on the inside of the pump. Next, remove the air filters, labeled "in" and "out." I found that one of the plastic bodies that holds the filters in place was broken, so I put two of them and filters on my parts list. The O-rings on the filter bodies were also cracked and needed to be replaced. You can see in the picture that the "out" port has carbon buildup around it (Figure 1, left). This was the broken filter body. A broken intake filter will allow dust into the blades, and a broken output filter can clog your muffler, which causes the motor to overwork itself (Figure 2, left, the old filter bodies; right, new filter bodies).


Next, remove the muffler and the intake hose. Take out the five bolts that hold the vacuum head cover on, and carefully pull the head cap off. If it's stuck, do not use a prying tool to get under the gasket. Use a rubber mallet and lightly tap on the head cap while supporting it with your other hand so it does not fall. It should pop off with just a few taps. Most likely you will need to replace the gasket, so put it on the list. Since you have taken the pump apart, it is a good time to replace all the minor parts. Use a razor blade to remove the old gasket. The inside is probably going to be rusty and dusty (Figure 3, left) so you will want to clean it with a wire brush and water then dry it off well.


 There will be six more bolts holding the head on. The head should come off once you remove them. If the head is stuck, tap it lightly with a rubber mallet to release it. Clean the head with a wire brush and water, and make sure to dry it thoroughly to prevent rust. At this point you will be exposing the inner working of the vacuum pump.  The spinning carbon blades are what make the suction happen.


The blades in our unit experienced a catastrophic failure and had broken; that's what caused the terrible noise before it stopped working (Figure 4, left). Remove the broken pieces with a screwdriver or pick, being careful not to scratch anything, and blow the dust out of the vacuum chamber. It is very important that all the broken pieces of the blades are removed, so use a flashlight to look thoroughly. Add blades to your list.


That should be the last of the parts you need, and this is as far as you should need to take the pump apart. It will take a few days for the parts to arrive so make sure that you don't lose your pieces while waiting.


Using 400-grit sandpaper, very lightly remove any surface rust from the moving parts, but do not apply any oil to the inside of the pump. Blow out the excess dust and rust. You can take this opportunity to blow the dust off the whole assembly, tank, and motor to ensure long life.


The carbon blades are curved on one edge. Be sure to fit them in the slots so the edges complement the circular shape of the spinner (Figure 4, right). With all four blades in place, rotate the spinner a couple of times by hand slowly to make sure they are moving properly. They should drop in the slot on the down stroke.


If everything looks good on the inside, you can now reassemble the head. Put the head back on and put the screws back in, cross-tightening them like you would wheel lugs for your car. Get them good and snug but be careful not to overtighten them. The Friddle's technician that I spoke to just snugs the screws down and does not use a torque wrench. He stated that typically for that size of bolt it would be about 20 inch-pounds of torque.


After the head is on, reassemble the head cover. I found it easier to tighten the intake hose while the head cover was off. Use Teflon tape on all the air fittings to prevent leaks and snug the hose in place. Carefully place the new gasket and the head cover, and then apply the screws (Figure 5). Cross-tighten the screws again to ensure even tightening. If your muffler looks dirty, soak it in thinner and then blow off any gunk. Apply Teflon to the threads and tighten the muffler in place.

The old filters will slide right off the body. Apply Teflon to the threads and slide the new O-rings into place, at the top of the body, and then the new filter. Just hand tighten the filter bodies back into place until they are flush with the head cover. They are somewhat fragile, so if you overtighten them you will immediately know it and have to replace them.


Finish cleaning the exterior and you will be ready for a test (Figure 1, right). Cross your fingers and plug it in. If everything was done carefully, your pump will be humming happily like before. Put the system back together and get back to work.


Travis Petersen, BOCP, COA, works at A.O.P. Orthotics and Prosthetics, Fayetteville, North Carolina, as a practitioner and clinic manager. He has also worked as a practitioner and technician for companies in Missouri. He can be contacted at