Vacuum Pump won't go

[Dean Center]

2 days ago, while sanding a bowl held on the lathe with my vacuum chuck, I completed the outside, turned off the pump, and when I turned it back on again, nothing happened. No sucking. I replaced the air filter, blew out the air lines, and checked the electrical connections. At some point of checking things out, I realized the pump would make a buzzing hum when I turned it on. The pump is in the next room, and when listening from that room, the sound was quite definite. (I made a recording of the sound, if hearing it would help) In any case, the electrons are apparently getting from the breaker panel to somewhere in the pump set up.

The pump is a common dual wobble piston pump which has a large, separate capacitor. It was used when I got it 5-6 years ago and I replaced the gaskets and valves at that time. I saw no Magic Smoke, and there is no goo on or under the capacitor.

Could those of you who are knowledgeable about electromechanical things suggest what might be wrong or how to proceed? While I'm not a whiz on electrical things, I've got experience solving other types of problems and fixing things. Also, there's no good electric motor shop around here.

Thanks for any assistance.

 

[Bill Boehme]

If the motor has a start/run capacitor some possible causes of a failure to start would be:

• A humming sound would be a good indication that the capacitor has failed.
• An open start winding could also cause a humming sound.
• A less likely cause would be the centrifugal switch not working.

If the motor is humming that is a good indication that the motor's run winding is still working. A stuck rotor is another remote cause of the motor humming, but not turning.

I believe that the motors used in small vacuum pumps typically don't have a high starting torque. What this means is that their normal operating condition is to start unloaded (not holding a high vacuum). This isn't the case for vacuum pumps designed for refrigeration systems.

 

[Chris Lawrence]

Checking that capacitor would be my first step. Google will tell you how to test a start capacitor with a multi meter or just replace it with the same size one. There not expensive.

 

[JeffSmith]

I've got a Thomas Riechle wobble piston pump like that - I use it with my carving stand. It had a similar problem a while back, just humming, no vac. Replaced the start capacitor - all good ever since. I will say, that pump is quiet and just keeps on going. Bought it for less than $40 on ebay, threw a $20 rebuild kit in it and it has been going strong for the last 15 years. It was used as an aeration pump for a water system

I've also got a gast rotary vane pump I use on the lathe - it, too has been trouble free.

 

[Dean Center]

Thanks for the replies. I was thinking it was a Thomas brand pump, so thanks for confirming, Jeff.

I pulled the capacitor. It did not discharge, as best I could tell. It looks dusty, but otherwise normal. When I went to test it with my multimeter, I realized I had taken it to our high school shop and won't be able to access it for a couple days. I've ordered a new capacitor online, but it'll take a while to get here. One of the local HVAC businesses might have something in stock that would work, but I couldn't check on the weekend.

The motor spins freely, and sucks when I do it by hand.

If it's likely the windings are OK, how do I check the centrifugal switch? (probably easy if your multimeter is not locked away for the weekend

 

[Vitor Cruz]

Modern single phase induction motors d’ont have centrifugal switch. Without capacitor and the other wires connected If you power the motor and help it to star the rotation it should rotate as normal. The capacitor is just need for the motor to start….

 

[Richard Coers]

The motor spins freely, does that mean the pump spins too?

 

[Dean Center]

Richard,
I hear the burble sound of the wobble pistons when I spin it by hand. (Obvously, much, much slower than when under power.) The pump doesn't actually spin. There's a clever gearing effect where the motor shaft drives a geared circle on the lower end of the piston rod, with a net effect like a cam shaft.

Here's a photo from Bill Noble's web site. Though it may not be exactly the same model, it's real similar.

 

[Bill Boehme]

If it's likely the windings are OK, how do I check the centrifugal switch? (probably easy if your multimeter is not locked away for the weekend

Your motor is likely to be the type that uses a start/run capacitor that is always in the circuit and doesn’t have a centrifugal switch. This type of motor would be used where a high starting torque isn’t needed. In order to check the centrifugal switch it is necessary to remove the rear cover plate from the motor. Here is what the one looks like in my first lathe which I rewired in order to reverse the motor.

 

[Dennis J Gooding]

I do not know whether is is relevant to your problem, but the motors on two of my woodworking machines failed to start because dust or chips lodged between the contacts of the centrifugal switch. I was able to dislodge it with compressed air.

 

[Dean Center]

Here's a brief follow up. On Tuesday I was able to get my multimeter and despite pretty good Youtube help, couldn't get understandable results on the capacitor. It still looked OK physically.

I had placed an order for a new capacitor with Supply House (excellent outfit, speedy response and decent prices) and received it today. I went out as soon as it arrived, plugged it in and the pump ran just fine!

Then I spent a half hour trying to figure out why my band saw wouldn't run. This time the multimeter suggested that something was wrong with one side of the double throw switch. Blowing it out didn't fix it. I pulled the switch out, took it apart, and discovered that one copper internal component had broken off on one side. Went in and ordered a new one of those.

We just had a heavy wet snow storm that broke many tree branches, so I've got a bunch of fresh wood to process. Gotta get all this stuff working!

Thanks for all your help.

 

[JeffSmith]

Good to hear the capacitor was the problem - simple solutions are great. When replacing switches and electrical components I try to upgrade to a better or more substantial part - mil spec if possible - I'm not an electrician and need all the help I can get keeping things running in my shop.