Shurflo Vacuum, how much?

Hey folks,

I'm working on a small shurflo 4008 vacuum system. I had read and seen videos of folks getting 20-23inhg, but I only seem to be getting 13-14inhg at the pump.

I've checked and resealed the only fitting between the pump and my gauge and it doesn't seem to make any difference. The interesting thing is that even if I isolate the pump with a ball valve on the either side of the pump and shut the pump off, it still looses vacuum. I'm starting to conclude that the pump housing itself has a leak. Current setup: https://imgur.com/a/CBGhDx5

Anyway, how much vacuum should I expect to get using this pump? Has anyone else run into an issue like this?

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Originally Posted by madmaples

Hey folks,

I'm working on a small shurflo 4008 vacuum system. I had read and seen videos of folks getting 20-23inhg, but I only seem to be getting 13-14inhg at the pump.

I've checked and resealed the only fitting between the pump and my gauge and it doesn't seem to make any difference. The interesting thing is that even if I isolate the pump with a ball valve on the either side of the pump and shut the pump off, it still looses vacuum. I'm starting to conclude that the pump housing itself has a leak. Current setup: https://imgur.com/a/CBGhDx5

Anyway, how much vacuum should I expect to get using this pump? Has anyone else run into an issue like this?

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Are you using the filter screen on the intake side of the pump that comes with some of the pumps? Those can leak vacuum if the bowl is not screwed on tight. Are you using a recirculating line? If you are not recirculating a little amount of liquid then you won’t get high vacuum. Also, make sure the screws that hold the pump to the motor and hold the 2 pieces of the pump housing are tight. I’m getting 20-25” of vacuum on mine depending upon how tight I am able to keep my tubing system. That’s on 110 taps with tubing that is now 12 years old.

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Originally Posted by BAP

Are you using the filter screen on the intake side of the pump that comes with some of the pumps? Those can leak vacuum if the bowl is not screwed on tight.

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Thanks for the tips, I've removed the filter for testing and that didn't change much.

Quote:

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Originally Posted by BAP

Are you using a recirculating line? If you are not recirculating a little amount of liquid then you won’t get high vacuum.

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I don't have a recirculating line, how does that work and where does it go? pulling a bit of sap back from the tank to the vacuum side?

Quote:

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Originally Posted by BAP

Also, make sure the screws that hold the pump to the motor and hold the 2 pieces of the pump housing are tight. I’m getting 20-25” of vacuum on mine depending upon how tight I am able to keep my tubing system. That’s on 110 taps with tubing that is now 12 years old.

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I'll have to check those screws again, I even tried to seal the split in the case with some sealant tape and that didn't seem to improve the vacuum.

The thing that has me scratching my head is that it's not just that I'm getting less than 15inhg with only a vacuum gauge attached, but as soon as the pump turns off the vacuum drops, which indicated to me that air is getting in somewhere.

After both you, BAP, and mapleflats on this thread pointed me to recriculation, I experimented a bit tonight with a ball valve to introduce just a tiny bit on the vacuum side and that made all the difference! I was holding steady at 26inhg on my test setup!

Quote:

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Originally Posted by madmaples

After both you, BAP, and mapleflats on this thread pointed me to recriculation, I experimented a bit tonight with a ball valve to introduce just a tiny bit on the vacuum side and that made all the difference! I was holding steady at 26inhg on my test setup!

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Diaphragm pumps can’t really pump air, they pump liquid. In order to make vacuum, they need liquid to be able to move what air is also in the line to eventually create a vacuum.

Quote:

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Originally Posted by BAP

Diaphragm pumps can’t really pump air, they pump liquid. In order to make vacuum, they need liquid to be able to move what air is also in the line to eventually create a vacuum.

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Yea, makes perfect sense, I had tried to introduce some liquid before, but hadn't thought about having a continuous trickle.