Rebuild hand held vac pump; re zero gauge

Recently I had the misfortune of sucking water into my pistol style vac pump. Slowly it began to lose vacuum so I decided to take it apart to determine if I could rebuild it. While taking it apart I dropped it on my work bench and the vac gauge needle jumped to 15 and stayed there.

PUMP REBUILD
These Chinese made vac pumps are found everywhere from Harbor Freight to Amazon and your local auto parts stores and cost as low as $20 to as much as $60. The only difference I have seen is how the pistol grip attaches to the barrel of the pump- it either has a threaded barrel which the pistol grip screws into or the barrel has a recess for a snap ring and the pistol grip screws onto the snap ring. The interior of the pumps can also be slightly different although the operating principle is the same.

I could go into detail on this part, but in my research I found a youtube video which did a great job so I suggest you view it. It is titled “Actron CP7830 Hand Vacuum Pump Rebuild”.

Actron offers an $8 repair kit with 2 O rings, 2 schrader valves and a check valve which is a round, flat piece of rubber on a stem.

I took mine apart, cleaned it, reassembled and tested it. It held better but still leaked. I suspect that the fluid stretched the flat rubber check valve which must replaced. My pump is not an Actron and while the repair kit may work for it, I decided to spend the extra $12 and order a new one.

RE ZERO GAUGE
The gauge must be off the vac pump for this step. If your gauge needle is only off a couple of inHg this may not be worth your time.

Remove the gauge cover or bezel face plate, then remove the two screws on the back of the case. Gently slide the gauge internals out of the case being careful not to hit the needle or gauge face. Holding the gauge by the threaded fitting, turn it over and gently place it on the work surface.

The third picture shows a side view of the gauge internals. You should see a small U shaped brass section connected to the other parts. Take a small pliers or needle nose and gently squeeze the U. Reducing the U will bring the needle towards zero. Turn over, check the needle position and repeat if necessary.

The second picture shows two U’s, one flat at the bottom and one in the middle pointing up. The middle one is the one you see in the third pic and is the easiest to adjust.

Note that there is a peg at the zero location to prevent the needle from going below zero. Ideally the needle should be close to but not touch the peg. If it touches simply take a small flat head screwdriver and gently gently spread the U out until the needle moves off the peg.

I settled for the needle being at 1 inHg as sufficient for my needs.

Once you are finished positioning the needle, carefully slide the internals back into the case, making sure the needle is not hitting the gauge face, insert and tighten the two screws in the back, install the cover plate and thread and tighten into the vac pump remembering to use thread tape.

Just for grins here are the pics of the pump internals. The third pic shows the flat rubber check valve I believe to be the source of the leak.

That flat rubber check valve and internals look icky. :) That’s your problem for sure. When I fix most anything and take it apart, my most common fix it clean it and reassemble and that does the trick, especially if you have new parts to put in.

The first time I put it back together I added a little grease, which was a mistake. I then cleaned and dried it and it did better, but still not holding vacuum. I may try to heat it up a little to see if the rubber will re form and seal. Something to do until the replacement arrives.

I should probably take apart the hand pump I have and try cleaning it out. I got water in it, something inside rusted and it doesn’t always want to return to the depressed position, though the gauge seems to be fine. I would have tinkered with it long ago, I just don’t really use it except to verify pressures for electric pumps.