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Dumb Vacuum Pump Questions

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IMO the only thing the vacuum pumps do is "boil" out the air that is dissolved in the oil. The problem with the air in the oil is it cavitates out as the oil flows thru the shock's valving and upsets damping. The high charge pressures help reduce cavitation but removing the entrained air from the oil gives you a head start.

So how much vacuum do you need ? IMO you need more vacuum than a air pump can provide. An air conditioning vacuum pump will pull almost all of the entrained air out of the oil, but a caveat is that in some situations it will draw air thru the shock seals (they are designed to seal the other way).

Here is a link to Robinair on vacuum, while I don't think you need the high vacuum of an high end AC vacuum pump for shock servicing the info in the link is useful.

http://www.robinair.com/acsolutions/acvacuum/acvacuum.php

Edited by chuck4788

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Hi. I´m building my vacuum pump with Air-vac UV143H vacuum generator, it´s capable of 29.7 inhg vacuum. My problem is I cannot find any suitable clear hose. I can buy tygon r3603, but only in size 1/4 I.D, 3/8 O.D that withstand only 20inhg vacuum. What other brand do you use?

Try this place, http://www.emiplastics.com/

Its where i got my plastic tubing and push lok fittings. I use the clear 1/4 (6mm) tubing, works fine and copes with -30 Hg no worries.

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Try this place, http://www.emiplastics.com/

Its where i got my plastic tubing and push lok fittings. I use the clear 1/4 (6mm) tubing, works fine and copes with -30 Hg no worries.

Just beware they bill for $100.00 when order is placed. It gets corrected before it actually comes out of your account. I assume their typical order is for several hundred pieces. When we order it's probably going to be under $50.00.

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A pic of my homemade vacuum shock filler after rebuilding a PDS shock. I have a venturi vacuum pump and it has enough vacuum to let the oil boil out all the air without pulling air trough the seals or destroying bladders of the KYB or showa shocks.KTM Willy 008.JPG

Edited by Freestyler

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You are supposed to use nitrogen in the shock, NOT HELIUM? :jawdrop: Or are you working on the space station?

Edited by KTM-Lew
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How loud is the venturi??

I really wanted to use one but I know they're loud

The vac pump is too loud for me sometimes!

Your setup looks good btw

Edited by ds1434

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hello, some days ago I finished my vacuum pump, is a transparent hose manufactured by FESTO. I want to thank this forum for the great help in planning the construction. sorry for my English, greetings from Argentina.

5e7180267aa44d60882b626ddc2b3feao.jpg

Edited by osiarg

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Do many others experience the shocks allowing air to enter via the seal head? I have a few times and its frustrating as it defeats the point of a vac pump system as you cycle and cycle and keep getting air, makes it hard to trust the setup

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Do many others experience the shocks allowing air to enter via the seal head? I have a few times and its frustrating as it defeats the point of a vac pump system as you cycle and cycle and keep getting air, makes it hard to trust the setup

Yeah ive had some trouble on a couple of older WP PDS shocks ive done that have a few hours on them, ie shaft seal not quite as new. Whereas the newer shocks ive done will cope with a bit more vac no problems. So for the older shocks where i notice air pulling through, I just drop the suction down to about -20 instead of the normal -25 to -29. Ive got a bleed on my vac pump suction line so i can adjust the suction.

Apparently a bit of o-ring/seal grease around the seal head when assembling can help with the initial bleed. Haven't tried this myself yet though.

Edited by yamaha227
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You don't need anymore than 20" once you start cycling.

Only on the initial vac cycle where you are simultaneously(dual line setup) degassing the reservoir and evacuating the shock do you need full vacuum.

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How loud is the venturi??

I really wanted to use one but I know they're loud

The vac pump is too loud for me sometimes!

Your setup looks good btw

It's my air compressor which is loud and is constantly on when I use the venturi because it needs a lot of air. I have a damper on my venturi and it is not noisy at all. It is a Scmaltz Venturi with digital vacuum reading.

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It's my air compressor which is loud and is constantly on when I use the venturi because it needs a lot of air. I have a damper on my venturi and it is not noisy at all. It is a Scmaltz Venturi with digital vacuum reading.

Nice, how much does something like that run??

Very interested especially with the dig readout!!

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The WP instruction for their vac pumps says:

1st cycle: 4 mbar

2nd cycle: 8 mbar

overpressure: 3bar

If you use full vac it sucks air from everywhere. When you bleed a KYB shock via the bleedwhole it also sucks over the N2 resi.

As a consequence the right vacuum pressure is crucial for a good result.

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Nice, how much does something like that run??

Very interested especially with the dig readout!!

They are not cheap. Normally they cost +400 euro.

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Yeah ive had some trouble on a couple of older WP PDS shocks ive done that have a few hours on them, ie shaft seal not quite as new. Whereas the newer shocks ive done will cope with a bit more vac no problems. So for the older shocks where i notice air pulling through, I just drop the suction down to about -20 instead of the normal -25 to -29. Ive got a bleed on my vac pump suction line so i can adjust the suction.

Apparently a bit of o-ring/seal grease around the seal head when assembling can help with the initial bleed. Haven't tried this myself yet though.

20-23mmhg does the trick for me as well. Anymore than that is chasing your tail. I thought it was my setup at first, check for leaks around the fittings

and such with no go then the thought of the seal came to mind.

Nice looking setups there!

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The WP instruction for their vac pumps says:

1st cycle: 4 mbar

2nd cycle: 8 mbar

overpressure: 3bar

If you use full vac it sucks air from everywhere. When you bleed a KYB shock via the bleedwhole it also sucks over the N2 resi.

As a consequence the right vacuum pressure is crucial for a good result.

Good post!

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hello, some days ago I finished my vacuum pump, is a transparent hose manufactured by FESTO. I want to thank this forum for the great help in planning the construction. sorry for my English, greetings from Argentina.

5e7180267aa44d60882b626ddc2b3feao.jpg

Very niiiiice!

  • Like 1

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