JST Posted September 28, 2015 Share Posted September 28, 2015 i am fitting an electric vac pump to gernate the brake servo vacuum on my TGV. (its has a through drive from the alt for current vac pump) alt is knackered and they are £££££££££££££ plus i like the idea of running it on a std alt where the A can be uprated easily. i believe the elec vac pump needs to switch in and out as required and as such i need a solenoid to control it. From what i haev found i need to maintain between 24 and 30"Hg in the servo. Does anyone have any idea on where i can get a vac switch/solenoid to turn the vac pump on and off as required. Do i also need a no return valve? Quote Link to comment Share on other sites More sharing options...
Boydie Posted September 28, 2015 Share Posted September 28, 2015 The electric vacuum pump I installed came with a vacuum switch, it turns the pump off once 22"hg is achieved (in less than 3 seconds) and switches it back on at 19"hg. You should be able to obtain a similar vacuum pressure switch at a drag racings parts supplier/specialist as naturally aspirated cars with "big high-lift cams" don't generate enough manifold vacuum to run a brake servo, so quite a few drag "funny" cars run electric vacuum pumps. If your pump doesn't have a built-in check valve I would advise you install one between the pump and the servo. Pump --- check valve --- vacuum switch --- brake servo. Make sure you use vacuum rated hoses as otherwise they will collapse in. Quote Link to comment Share on other sites More sharing options...
western Posted September 28, 2015 Share Posted September 28, 2015 there's a non return valve already fitted to the servo, where the hose connects. to stop any loss of vacuum from the servo. Quote Link to comment Share on other sites More sharing options...
Boydie Posted September 29, 2015 Share Posted September 29, 2015 Western true --- but ideally for an electric vacuum pump system there needs to be a check valve after, (or internally in the pump) and before the servo in the vacuum line where the pressure/vacuum switch is located so that it reads the vacuum in the system and reacts/switches accordingly. If there isn't one installed and the vacuum pump constantly loses vacuum the pressure switch will cause the pump to never turn off even though there is adequate vacuum in the servo for effective brake operation. The beauty of the electric vacuum pump system is that on long straight roads where you are seldom if ever breaking the pump, once it has achieved the required system vacuum, simply doesn't run. The failure of the standard Wabco mechanical pump design is that it is constantly evacuating the system, even though it may have achieved the required vacuum. Consequently a vacuum develops in the discharge chamber of the pump and oil is sucked past the piston and into the discharge chamber, it is then hydrauliced by the piston and hence the constant oil weep from the sealing welsh plug. It's a urine weak design Quote Link to comment Share on other sites More sharing options...
JST Posted September 29, 2015 Author Share Posted September 29, 2015 thanks guys, i will do some more digging aimed towards the drag guys Quote Link to comment Share on other sites More sharing options...
JST Posted September 29, 2015 Author Share Posted September 29, 2015 i am not getting very far with this, dont suppose an egr vac solenoid works on similar pressure? anyone know? Quote Link to comment Share on other sites More sharing options...
Boydie Posted September 29, 2015 Share Posted September 29, 2015 Not a clue, but I would very much doubt it. You need a vacuum switch with a range of ON at 19" hg and OFF at 22" hg, if you are not able to obtain one then I would look at replacing your current vacuum pump with one that has a built-in switch and check valve. Quote Link to comment Share on other sites More sharing options...
HoSS Posted September 30, 2015 Share Posted September 30, 2015 These electric vac pumps (as far as i know) are not rated for 100% duty. On most cars they are just to assist the primary pump on low revs etc. I use one from a XJR as a backup, and it get real hot if you leave it on. So your idea of switching it is valid i think. also the less leaks in the system, the less it will need to run. Check valves - agree. I use 2 gauges (vac & obd pressure) which display the value, with an alarm if low and an output to switch the pump off. http://file:///C:/Users/paharwoo/Downloads/Keyence%20-%20AP-30%20Series%20Pressure%20Switch%20Manual.pdf AP-31 is the vac model. You can find these on ebay for as little as 20gbp Quote Link to comment Share on other sites More sharing options...
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