vacuum pump spins backwards when turned off

[dhbiker1]

I finally wired the motor and fired it up and as soon as i pulled the plug, it spun backwards a few spins before i grabbed the belt risking my hand over breaking something. I will list the setup and try to include all details that could possibly cause this but I am unsure why this is happening.

De Laval Model 74 with vacuum tank below it and Leeson 3/4 hp motor
-there is a muffler with some sort of flapper that has a grease fitting
-I only had about 2 ft of pvc out from the tank. It goes tank - 3/4" pvc - tee w/ vac gauge - tee w/ regulator - 3/4" swinging gate brass check valve from home depot - capped off to test for now.

I used both the bascom's regulator and a de laval weighted regulator. Does anyone know the min vacuum you can get with the bascoms because I opened it as much as it would go and the vac just kept building. I then put in the de laval and it was keeping it steady at 15.5".

Am I missing something here? I don't want to do it too much and risk breaking something.

[royalmaple]

Put a check valve on the inlet side of the pump. That way when you run the pump it will draw through the check valve, but when you shut the pump off air can't come through and turn the pump backwards.

[dhbiker1]

maybe i wrote that confusing, there is a check valve on the inlet side of the pump. I went in order from pump inlet - first gauge then regulator then check valve. Also it happened with both the de laval regulator (you could hear the air escape) and the bascoms regulator (you couldn't hear the air escape)

[royalmaple]

You'd need 1 of two things, a section of pipe after the check valve that also has a cap on it. So that section of tubing would get under vacuum, then when the pump turns off there is vacuum on the other side of the check valve holding the check valve closed, thus not allowing the pump to rotate in reverse. Or take the check valve off if you are just testing it, then before you hook up to your system put the check valve back in. During testing the check valve isn't doing anything for you, you only want that in place when your setting it up to actually run it on your tubing.

Or you need a valve inbetween the check valve and the pumphead so you can open it before you turn the pump off. basically breaking the vacuum so the force of the vacuum won't draw the pump to spin backwards as well.

Make any sense?

[maplekid]

wouldnt the compression in the cylinder keep that from going backwards

[royalmaple]

That is a rotary vane pump.

[dhbiker1]

makes sense but wasn't it the same as having no check valve if i capped it right at the end of the check valve. It seems like the space in the tank that was under vacuum needs to be filled and the only way for that to happen is for air to come in from the exhaust side because the inlet side is really almost a controlled volume minus the regulator.

[royalmaple]

You got my head spinning now.

Are you using the tank below the pump head? Is that capped or just open? If it is open and you are putting vacuum on it after a check valve then it should not be holding any vacuum.

If you don't have the line going to the tank, then you would add a section of pipe and a cap to that. Then that acts like your tubing system(in theory) and vacuum will quickly rise since it is a very small and tight system. THen when you shut the pump off the vacuum in that system is going to hold the check valve closed, it want to pull the pump backwards but can't since the check valve is being sucked closed by the tubing system. Then as air enters the system through a valve or leaks the vacuum in the tubing system will get to zero and there will be no draw on the pump to turn it over backwards.

Is that what you are doing now or am I just explaining something you don't need to know or does not apply?

[royalmaple]

have you seen any of my pictures to see how I have my pumps set up?

[brookledge]

In my case I have a rubber flapper on the exhaust pipe in adition to a check valve going to the releaser. I have a small vacuum tank under the vacuum pump and motor. So when I shut the power off the flapper holds the vacuum back so the pump does not run backwards.
Keith

[dhbiker1]

Ok, so the air is coming back in because there is no check valve between the pump head and the vacuum tank below it. The exhaust does have some kind of flapper and a grease fitting. I will guess it has this to stop the back flow i am describing, but maybe it is worn out. I will look into that or just make up a flapper to put on it.

* I just added 2 photos to yahoo photos (they are from before i had the plumbing done but it shows the tank to pump and exhaust.)

[Russell Lampron]

I Teed in a ball valve on the suction side that I open when I shut the vacuum pump off. This keeps the pump from spinning backwards and there is no guess work as to weither a check valve is going to do it's thing or not. I am not sure about the Delaval 74 but I do know that they don't make vanes for the 73's anymore.

Russ

[ennismaple]

When you turn the pump off all you need to do is put your foot on the pulley to keep it from spinning backwards. After a few seconds it won't wan to spin anymore. We use Zero milk tanks so another method is to take a cap off of one of the lids before turning the pump off to release the vacuum.

[maplecrest]

jason nice pictures of tucks. dont get there any more sugaring is in the way of that fun. you need to put a check, swing valve betweem the releaser and the pump and tank. go to a plumbing wherehouse and get a 11/2 plastic swing check and that will solve your problem. if you insist on using that piece of junk that you bought from bascoms put it on the releaser. i have one plumbed into a vac tank for when it freezes at night to release. that is the only time it has worked for me. jeff