# Vacuum problem



## JRP3 (Mar 7, 2008)

My brake vacuum pump system won't hold a vacuum unless I hold my finger over the pump exhaust after it shuts off, then it will hold it until I let go. I have a new Summit tank with a check valve in the system. Bad check valve maybe?


----------



## zwmaster (Nov 23, 2009)

JRP3 said:


> My brake vacuum pump system won't hold a vacuum unless I hold my finger over the pump exhaust after it shuts off, then it will hold it until I let go. I have a new Summit tank with a check valve in the system. Bad check valve maybe?


I would say, definitely, bad check valve.
Hit it with a hammer


----------



## JRP3 (Mar 7, 2008)

Checked the check valve, it seems to be working. If I blow into the tank towards the vacuum pump air comes out the pump exhaust. If I try sucking air from the tank I can't. It seems as if I need a check valve on the pump exhaust but that doesn't seem right. The way my setup is now, from the front of the car, is brake booster->5 feet of hose->tank inlet->tank outlet with valve->5 feet of hose-> vacuum pump. Thoughts?


----------



## zwmaster (Nov 23, 2009)

Could it be that the check valve is build for higher pressure and won't close at sub bar pressures (or vacuum)? 
Try slowly to suck/blow into valve.


----------



## JRP3 (Mar 7, 2008)

I would think the pump pulls much higher vacuum than I can, but I'll try it.


----------



## zwmaster (Nov 23, 2009)

One other thing I can think of is to use standard workshop compressor with pressure regulator to test the valve for correct operation.


----------



## JRP3 (Mar 7, 2008)

Good suggestions. My pump was pulling about 15 in. Hg of vacuum, I adjusted it to about 20 in. Hg, still same problem. Put an air hose on the check valve and it engaged around 25 psi, which is 51 in.Hg! Don't know what a normal brake system runs at but that sounds high, so I'm guessing a faulty valve.


----------



## zwmaster (Nov 23, 2009)

JRP3 said:


> Good suggestions. My pump was pulling about 15 in. Hg of vacuum, I adjusted it to about 20 in. Hg, still same problem. Put an air hose on the check valve and it engaged around 25 psi, which is 51 in.Hg! Don't know what a normal brake system runs at but that sounds high, so I'm guessing a faulty valve.


Breaks should run around -650mBar or -65kPa if that's wrong then i'm buying worng pump for my build . 20inHg should be ok.


----------



## RKM (Jun 9, 2008)

JRP3,

I had a similar problem with vacuum. It would lose vacuum in about 30 seconds and the pump would cycle again. Turned out to be a leak in a remote vacuum switch. My system has a vacuum switch connected to the reservoir by a small poly tube. Pinching off the tube confirmed where the leak was. I was unable to seal this switch, but a replacement solved the problem.

Good luck.

Rob


----------



## JRP3 (Mar 7, 2008)

I found a reference that said normal vacuum is between 16-22 in.Hg.
RKM I'll look into that but since my system will hold pressure if I plug the pump exhaust, and the switch is before that of course, I don't think it's the switch.


----------



## RKM (Jun 9, 2008)

JRP3 said:


> I found a reference that said normal vacuum is between 16-22 in.Hg.
> RKM I'll look into that but since my system will hold pressure if I plug the pump exhaust, and the switch is before that of course, I don't think it's the switch.


Oops. Wasn't paying attention.


----------



## JRP3 (Mar 7, 2008)

Still a mystery. Played around with it a bit more, sucking on the storage tank I can draw about 1 inHg of vacuum and the check valve closes, so why did it take almost 25 psi blowing in the other side to close the valve? Here's my thought. Atmospheric pressure is around 15 psi I think, so when using air pressure you need at least 15 psi just to equal the pressure on the other side of the valve, then some extra to get it closed. When pulling a vacuum you've already got 15 psi so you just need to get enough of a differential to activate the valve. So I think my valve is working properly, I don't seem to have any leaks, yet I'm not holding pressure  I may try a different placement of the tank, closer to the pump, or farther away, to see if that makes any difference, but in a closed system I don't see how it would.


----------



## EV-propulsion.com (Jun 1, 2009)

got to be something like the vibration of the pump is causing the checkvalve not to seat 100%, even though it works out of the system. I would replace the checkvalve. I have seen some checkvalves that don't always seat-the kind with a flat "puck" inside. Do you know which kind you have?
Oh, still surprising, because some pumps don't even need a checkvalve -the valve in the pump does the job. (you would still use a checkvalve at the brake booster)
Mike
www.EV-propulsion.com


----------



## JRP3 (Mar 7, 2008)

The pump shuts off when it reaches pressure so I wouldn't think any vibration is preventing the valve from closing, plus the pump is about 5 feet away from the tank and valve. I don't know if the pump has it's own check valve or if it's working if it does, the system leaked down before I installed the tank and check valve. There is a valve on the booster of course. I'm tempted to slap a valve on the exhaust of the pump since using my finger as a valve seems to solve the problem. I'm using this tank and valve









http://www.summitracing.com/parts/SUM-G1464/?rtype=10


----------



## dtbaker (Jan 5, 2008)

can you sketch a 'schematic' as to where the pieces are in the loop? I would also suggest a little teflon pipe dope on all the hose barbs, and double check all hose clamps. you *should* be able to hold vacuum overnight with no visible loss.

other than a tiny leak at a fitting.... it is common that the pump itself 'leaks' when it is not running, hence the checkvalve 'downstream' of the pump, and before anything else.


----------



## JRP3 (Mar 7, 2008)

I'll double check again for leaks, but if I had a leak it wouldn't hold pressure when I hold my finger over the pump exhaust. Here's a schematic. Booster to tank with check valve to pump, total system about 10 feet long.


----------



## JRP3 (Mar 7, 2008)

Moving the tank and valve right next to the booster and then right next to the pump made no difference.


----------



## dtbaker (Jan 5, 2008)

JRP3 said:


> I'll double check again for leaks, but if I had a leak it wouldn't hold pressure when I hold my finger over the pump exhaust. Here's a schematic. Booster to tank with check valve to pump, total system about 10 feet long.


I'd have to suspect a leaking fitting.... you should be able to draw the vac down, and DISCONNECT the vac pump, and hold the vacuum... wait a sec, where is your vac switch?


----------



## JRP3 (Mar 7, 2008)

Switch is on a "T" right at the pump, forgot to draw it in. I still don't see how the system could have a leak, if it did putting my finger on the pump exhaust would still allow the system to leak down, but it doesn't. Admittedly I'm not standing there for more than a minute or so, I'll try sealing it off and seeing what happens over time.


----------



## etischer (Jun 16, 2008)

If your leak is though the vacuum pump exhaust port, the valve in the pump is faulty. Seems like your check valve is also faulty.  Perhaps there is some contamination in your vacuum booster. Getting any dirt on the reed valves in the pump will cause them to leak.


----------



## tomofreno (Mar 3, 2009)

If you have compressed air, you might blow through the check valve in case there is some dirt in it. Barb fittings should not require any sealant if the hoses fit tightly over them. Sure sounds like a bad check valve. As you say if it were a fitting it wouldn't hold vacuum when you place a finger over the hose. Atmospheric pressure is 14.7 lb/sq inch. The little pump probably evacuates to about 1/10 that pressure. Could be a leaky connection between the valve and tank, but then it wouldn't pass your finger test. You could disconnect the check valve from the tank, put your finger over the valve, pull a vacuum with the pump and see if it holds. Teflon tape on the threads should give a good seal when you re-insert it. I've used it to hold vacuum at 1e-6 Torr or 1.47e-5 psi.


----------



## dtbaker (Jan 5, 2008)

JRP3 said:


> Switch is on a "T" right at the pump, forgot to draw it in. I still don't see how the system could have a leak, if it did putting my finger on the pump exhaust would still allow the system to leak down, but it doesn't. Admittedly I'm not standing there for more than a minute or so, I'll try sealing it off and seeing what happens over time.


?? switch should be between tank and booster. check valve should be between tank and pump... if plugging pump exhaust port works, then your check valve is NG.


----------



## JRP3 (Mar 7, 2008)

I didn't think it mattered where the switch was, vacuum should be the same throughout the system shouldn't it? I can relocate it but the switch dose seem to be functioning properly.
I agree it must be a faulty check valve, but whenever I pull the tank out of the system and suck on it the valve closes right up, at less than 1 in.Hg.
I don't get it.


----------



## Jimdear2 (Oct 12, 2008)

JRP3 said:


> I didn't think it mattered where the switch was, vacuum should be the same throughout the system shouldn't it? I can relocate it but the switch dose seem to be functioning properly.
> I agree it must be a faulty check valve, but whenever I pull the tank out of the system and suck on it the valve closes right up, at less than 1 in.Hg.
> I don't get it.


Possibly the compression from the grommet in the tank or the hose clamp (if you are using one) is distorting the check valve when it is installed. Those valves are pretty cheap. I would try a new one.


----------



## JRP3 (Mar 7, 2008)

Actually I pull the whole tank and valve with hose attached out of the system to test it as a unit. I'll grab another check valve and see what that does.


----------



## etischer (Jun 16, 2008)

I agree, switch should measure tank pressure, not pump pressure. Who cares if the pump looses vacuum, that is what the check valve is for, to keep vacuum in the tank. Moving the pressure switch to the tank should reduce the number of times your pump is getting cycled. 



dtbaker said:


> ?? switch should be between tank and booster. check valve should be between tank and pump... if plugging pump exhaust port works, then your check valve is NG.


----------



## jehan12413 (Feb 4, 2010)

A simple way to check it would be to disconnect the pump from the hose after it shuts off and see if air is being sucked in the hose. If yes then its the check valve, if no then it's a leak somewhere else in the sysyem.


----------



## blackpanther-st (Apr 4, 2009)

I agree with etischer, the switch should be on the reservoir tank. the valves in the pump are high speed valves to deal with the rapped differentials the pump creates during operation; they are not designed for a solid seal of long duration, that is what the external check valve is for. 

most likely your reservoir vacume is holding, but with the swich on the pump side of the check valve, it is sensing the back seepage through the pump and is reengaging the pump to draw down between the pump and check valve. this explaines why his finger on the pump exoust stops the reentry. (If this is the cace the draw down time shuld be relitivly short as compared to drawing the entire reservoir the first time.)

Relocate your switch to the reservoir side of your check valve and you should be fine.


----------



## JRP3 (Mar 7, 2008)

Problem is the tank is not holding pressure, the gauge on the tank drops quickly. I'll relocate the switch and see what happens, plus I picked up another tank valve, just in case.


----------



## blackpanther-st (Apr 4, 2009)

If your gage is reading your tank, then you are probably right about the check valve being bad, but I would still recommend moving the switch as mentioned before to get the correct vacuum reference to it.


----------



## JRP3 (Mar 7, 2008)

The saga continues. Replaced the check valve in the tank, no change. Moved the switch inline between the tank and the booster, still won't hold pressure, but now the pump keeps running unless I tap or squeeze the switch, then it shuts off, system leaks, comes on again, etc. So the switch is bad. Don't know if trying to adjust the pressure messed it up or what. System will still hold pressure if I hold my finger over the pump exhaust, so I have no confidence that replacing the switch will solve the pressure issue. Anyone recommend a pressure switch? This one is setup through a relay so it doesn't need to handle much amperage.


----------



## david85 (Nov 12, 2007)

rctous sold me a vacuum switch for my car. I haven't used it yet, but he has been using them for a while and I do trust brian.


----------



## JRP3 (Mar 7, 2008)

Do you have a brand and part number? Brian's been MIA for a while.


----------



## david85 (Nov 12, 2007)

http://www.anver.com/document/vacuum components/vacuum-switches/vsel-adj-ncno!.htm


----------



## JRP3 (Mar 7, 2008)

Turned down the adjusting screw on the pressure switch and it's shutting off properly now. My feeling is that the internal valve on the pump must be leaking slowly enough that the valve on the tank isn't closing off because there isn't enough of a pressure differential. I'm trying to find a diagram of the pump, I think it's a Thomas, don't have it in front of me right at the moment.


----------



## dtbaker (Jan 5, 2008)

I think ALL the pumps have some leak-back... always need a check-valve 'upstream' to prevent leaking.


----------



## JRP3 (Mar 7, 2008)

That's the thing, I do have a check valve upstream, and it won't close off when the pump is in the system. I even replaced the check valve with another, same thing. Draw a vacuum, pinch off the hose, unhook the pump, release the hose, it holds vacuum. Put the pump back in the system, draw vacuum again, check valve won't close.


----------



## JRP3 (Mar 7, 2008)

It's acting as if there isn't enough leak back to force the valve closed.


----------



## few2many (Jun 23, 2009)

Really hate to ask this question, try not to take offense, is the check valve facing the right way? The arrow should face the pump, not the tank. could be some trash in check valve, vaccuum pump coul have bad reed valves.
Have you individually isolated and tested the components, or tested as a whole system?


----------



## tomofreno (Mar 3, 2009)

> It's acting as if there isn't enough leak back to force the valve closed.


 Seems it could be...if the check valve is just a bit sticky, or has too much inertia, and the leak back through the pump is very small. How 'bout if you mount the check valve so gravity assists in closing it?


----------



## JRP3 (Mar 7, 2008)

Few2many,
No offense taken, I'll take any suggestions, but I did explain that the system will hold vacuum if I disconnect the pump, so the valve must be working and must be facing the correct way. Plus it's a tank mounted valve and can only go in one way.
The pump is Thomas 107cdc20-898E but I can't find any parts list or exploded diagram for it.


----------



## JRP3 (Mar 7, 2008)

tomofreno said:


> Seems it could be...if the check valve is just a bit sticky, or has too much inertia, and the leak back through the pump is very small. How 'bout if you mount the check valve so gravity assists in closing it?


It's a tank mounted valve, I suppose I could try rotating the whole tank as a test, but this is the second valve I've tried.


----------



## JRP3 (Mar 7, 2008)

Found a diagram and parts list, but when I click on "View larger image" I get a blank page http://www.grainger.com/Grainger/rp...ria=20008600&search.x=1&exact=yes&from=detail

Can anyone else see the larger image?


----------



## dtbaker (Jan 5, 2008)

this is just plain strange.... I bet you're getting pretty frustrated! Can we step back to square one and verify your plumbing looks like:

brakebooster ----vacRes---vacSwitch--checkValve--vacPump


----------



## JRP3 (Mar 7, 2008)

dtbaker said:


> this is just plain strange.... I bet you're getting pretty frustrated! Can we step back to square one and verify your plumbing looks like:
> 
> brakebooster ----vacRes---vacSwitch--checkValve--vacPump


Actually it is now
brakebooster ----vacSwitch---vacRes--checkValve--vacPump
Originally it was
brakebooster---vacRes---checkValve---vacSwitch---vacPump
It can't be done the way you have it laid out since the check valve is mounted on the tank, no way to put the switch between the tank and the valve, not sure there is a reason to do it that way anyhow.
The system held pressure overnight only dropping 3 inHg, after I pulled a vacuum, pinched the hose, disconnected the pump, un-pinched the hose, hooked the pump back up and let it sit there. Definitely not a leak in the system.


----------



## zwmaster (Nov 23, 2009)

JRP3 said:


> Actually it is now
> brakebooster ----vacSwitch---vacRes--checkValve--vacPump
> Originally it was
> brakebooster---vacRes---checkValve---vacSwitch---vacPump
> ...


Is it possible to put check valve on exaust of the pump?


----------



## JRP3 (Mar 7, 2008)

That's my next step. I actually did try that earlier but didn't have enough hose clamps to make a good seal. The check valve would not close, unless I put my finger over it for a few seconds, then pulled it off quickly so that it "popped", then the valve would close.


----------



## dtbaker (Jan 5, 2008)

JRP3 said:


> Actually it is now
> brakebooster ----vacSwitch---vacRes--checkValve--vacPump


this *should* work as the check valve is first in line upstream from pump.



JRP3 said:


> Originally it was
> brakebooster---vacRes---checkValve---vacSwitch---vacPump


this I could predict would NOT work as any leakback from pump would 'fool' the switch and turn on pump even when pressure in res is propably fine.


----------



## tomofreno (Mar 3, 2009)

> Can anyone else see the larger image?


 In the window that opened when I clicked the small image, there was a small square in the upper left corner. Clicking on it leads you through downloading some Javascript sw which is required to see the image. Mine failed to load automatically. Then it gave me the option to do it manually, but I didn't care to do it. If you can't get it to work I'll try the manual install to see if I can open it.


----------



## gdirwin (Apr 7, 2009)

Can you install the check valve backwards, pump it up with air from a compressor, then stick it under water to see where the leak is?


----------



## JRP3 (Mar 7, 2008)

tomofreno said:


> In the window that opened when I clicked the small image, there was a small square in the upper left corner. Clicking on it leads you through downloading some Javascript sw which is required to see the image. Mine failed to load automatically. Then it gave me the option to do it manually, but I didn't care to do it. If you can't get it to work I'll try the manual install to see if I can open it.


Thanks, I got it, had to install a Java update. Unfortunately the parts list numbers and descriptions don't match up with the image. My pump did not come with 31,32,33 which may be muffler?


----------



## JRP3 (Mar 7, 2008)

gdirwin said:


> Can you install the check valve backwards, pump it up with air from a compressor, then stick it under water to see where the leak is?


Do you mean stick the pump underwater? Don't think I'll try that, though I could try soaping the diaphragm seal.


----------



## dtbaker (Jan 5, 2008)

JRP3 said:


> Do you mean stick the pump underwater? Don't think I'll try that, though I could try soaping the diaphragm seal.



I think he's talking about the inner tube in the bathtub diagnostic technique. NOT the pump underwater, just the res tank and check valve with above atmospheric pressure to look for bubbles.

The pump leaking should be completely out of the equation since it is downstream of the check valve.


----------



## JRP3 (Mar 7, 2008)

The only leak is in the pump, as the system held vacuum overnight when I disconnected the pump.


----------



## JRP3 (Mar 7, 2008)

Picked up a new check valve: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=180492954737
Solved the leak down problem. The difference with this valve is it's closed in it's normal state where the others required a pressure differential to close.


----------



## Jimdear2 (Oct 12, 2008)

JRP3 said:


> Picked up a new check valve: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=180492954737
> Solved the leak down problem. The difference with this valve is it's closed in it's normal state where the others required a pressure differential to close.


 
HOO RAY . . . WOOPIE . . . Glad to hear it.

The flap valves in the diaphram pump must have had just a small leak but the pressure differential never got high enough to close the valve. 

Isn't afterthought engineering great. See how easy it was to figure out the cause of the problem after you fixed it.


----------



## dtbaker (Jan 5, 2008)

JRP3 said:


> Picked up a new check valve: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=180492954737
> Solved the leak down problem. The difference with this valve is it's closed in it's normal state where the others required a pressure differential to close.



wow, thats a detail that would be easy to miss in putting together a 'kit'. glad you tracked it down. there must have been 'enough' vacuum in the line between the valve and pump to not set the valve as the pump gradually leaked as expected.

I have had no prob with mine purchased as kit from KTA, but not looked to see if it is similar to the one you had problems with, or the one that works.


----------



## JRP3 (Mar 7, 2008)

Some of the EV places sell the same Summit tank, valve, and gauge that I bought from Summit.


----------

