Troubleshooting a Vacuum Bag Leak

Problems with vacuum pump operation in vacuum-bag veneering may be traceable to a leak in the bag. May 13, 2013

I have a ten year old vacuum pump that I bought from Woodworkers Supply. It is the standard pump that I see in most wood shops that use vacuum bags to veneer tables and other furniture parts. The problem is that even when I adjust the point where the automatic shutoff should turn the pump off, it keeps running. I have to adjust it to a very low pressure to turn it off, then when I adjust it back to a normal pressure, it won't shut off when it reaches that level. Is there somewhere I can put a replacement shut off control?

Forum Responses
(Veneer Forum)
From John Van Brussel, forum technical advisor:
Make sure there is nothing in your hose or connectors restricting airflow. Also if you have filters on the back of the pump, you can remove them and clean or replace them.

From contributor J:
I'm unfamiliar with the Woodworker's Supply unit, but I'm guessing it's similar to those sold by VacuPress and others. I would bet that VacuPress could help you. I've also talked with Mike Hamilton of Vacuum Laminating Technology, and I know he had such a controller available. I believe its price was in the $25 range.

From contributor O:
It may not be your pump; it may be your bag. Check the vacuum integrity of the bag. If you have a hole or small leak, it will turn your pump on and off and apply different HG to your bag. I was taught 25 years ago never to put the HG gauge on the pump. You know what it's pulling. Put the gauge on the bag.

From the original questioner:
Thanks everyone. I disconnected the pump from the bag, cleaned the filters and checked the tubing for obstructions. Then I ran the pump while it was still disconnected from the bag. It worked fine. It cycled on and off many times just like it should. I think the problem is with the bag. There must be some kind of intermittent slow leak. I'll have to hunt it down.

From contributor O:
Hook up your bag to the pump. When you have reached max HG, take a spray bottle and add soap and spray the bag. You will see bubbles appear. Or put your ear to the bag - you will hear it leak. I cannot stress enough how crucial it is to have a gauge on the bag, not the pump. I feel the manufacturers are being a little misleading. I have been doing vacuum work for over 27 years in the aviation and furniture making world, and I haven't seen a better solution than the gauge on a bag. Look at for gauges, fittings and bags, and sealant tape.