Vacuum Dashpot - PeachParts Mercedes-Benz Forum

Biodome · #1 10-03-2006, 07:43 PM

Quick question. I was wondering if the vacuum dashpot was only a single way valve. Should I be able to blow air through it and suck air into it or is it a one way valve?

kip Foss · #2 10-03-2006, 10:55 PM

The vacuum pots are designed to work on vacum-hence the name, but I immagine that they will work with pressure. The problem is that they are designed to work with a max. of 14 psi external press. If you subject them to internal press. you stand a good chance of blowing the diaphram off the end.

Lostyankee · #3 10-03-2006, 10:55 PM

Are you talking about the vacuum check valves? Example: on a 300 SD there are two check valves (blue on black plastic) that control the door lock function and yes these are one way check valves. BTW: these are very easy to break so watch out or $10 each.

Samuel M. Ross · #4 10-04-2006, 03:15 AM

... yes the vacuum diagram for your model MBZ..
see http://www.peterschmid.com/vacuum/1977_1985/616_617_91/616_617_91.jpg
has what is shown as #72 and called a vacuum surge damper but this is also commonly known as a "dashPot". Many parts house even know and sell them as "check valves" but THE ARE NOT a CHECK VALVE... and they do not have any internal diaphragm. They are a simple air/vacuum chamber with the connectors on each end possibly serving as restricted orifices. This vacuum components are installed primarily to retard/dampen the otherwise harsh 1-2 shift on automatic trannyies. I just tested one on both our 1980 240D and 300D [ not in these car's original design] and so my experience with them is fresh, but positive. They only cost $4 -to- $10.
You should be able to blow through them and not cause any damage for there is nothing inside to damage and I don't think your lung-power is enough to damage them... it is just a hollow chamber that acts to delay the vacuum bleeding action of the Vacuum Control Valve [VCV] on the IP. The VCV is the component most responsible for simulating throttle pedal position by controlling the vacuum signal that is sent to the vacuum modulator on the auto tranny.
Good luck,
Sam

Stevo · #5 10-04-2006, 12:09 PM

Soo thats what a "dashpot" is, thank you, I've wondering about that since that last thread

Guess my 240Ds dont have any.

Samuel M. Ross · #6 10-04-2006, 12:29 PM

Quote:

Originally Posted by Stevo

Soo thats what a "dashpot" is, thank you, I've wondering about that since that last thread

Guess my 240Ds dont have any.

Stevo,
Looking at your Signature list of VEHs I note that you have a couple of MBZs that are "stick shift". There might be a different kind of "DashPot" that was installed or might be useful on these cars... however I think these are connected in the mechanical linkages of the IP and retard the throttle directly and have nothing directly to do with your manual trannies!

Sam

Stevo · #7 10-04-2006, 06:45 PM

Quote:

Originally Posted by Samuel M. Ross

Stevo,
Looking at your Signature list of VEHs I note that you have a couple of MBZs that are "stick shift". There might be a different kind of "DashPot" that was installed or might be useful on these cars... however I think these are connected in the mechanical linkages of the IP and retard the throttle directly and have nothing directly to do with your manual trannies!

Sam

Yes, actually there is a "dash pot" on the throttle linkage of my "85", I'm learning all kinds of thing today

rocketman93116 · #8 10-04-2006, 12:40 PM

My understanding of a dash pot as it pertains to an automotive application is typically a spring loaded mechanical device that pushes or pulls an arm or linkage (e.g. carburetor choke pull off ect.) with an opposing force applied by vacuum or pressure. On the Mercedes the most common use of a “dash pot” that I have seen is in the climate control system for the vent door(s) controls.

A check valve is basically a vacuum delay valve that holds off vacuum or pressure for a calibrated pre determined amount of time and or lowers the amount of vacuum supplied to the component by reducing the size of the the orifice through which the vacuum passes.

A handheld vacuum pump tester with gauge is indispensable to check any vacuum related system.

Samuel M. Ross · #9 10-04-2006, 01:56 PM

Quote:

Originally Posted by rocketman93116

My understanding of a dash pot as it pertains to an automotive application is typically a spring loaded mechanical device that pushes or pulls an arm or linkage (e.g. carburetor choke pull off ect.) with an opposing force applied by vacuum or pressure. On the Mercedes the most common use of a “dash pot” that I have seen is in the climate control system for the vent door(s) controls.

A check valve is basically a vacuum delay valve that holds off vacuum or pressure for a calibrated pre determined amount of time.

A handheld vacuum pump tester with gauge is indispensable to check any vacuum related system.

Rocketman,
Wikipedia, the free OnLine encyclopedia agrees more with you than me!
Check out their definition at: http://en.wikipedia.org/wiki/Dashpot
"A dashpot is a mechanical device, a damper which resists motion via viscous friction. The resulting force is proportional to the velocity, but acts in the opposite direction, slowing the motion and absorbing energy. It is commonly used in conjunction with a spring (which acts to resist displacement)."

And as I stated before MBZ calls this vacuum chamber a "surge dampener".

Maybe we need a "Glossary of Terms" for the WebSite/FORUM... for many times I have seen where we get caught up in terms... and this is proof that this includes myself as well. I have seen parts sources call this a "dasPot" and so that's what I started calling it. There are different names used for many different vacuum parts on these Vintage MBZs and some of this I'm sure is due to translation problems.

Sam