VACUUM PUMP FAILURE! Are you neglecting yours?? - Page 7 - PeachParts Mercedes-Benz Forum

vstech · #91 06-23-2012, 09:10 PM

Quote:

Originally Posted by whunter

There is none.

.

yeah... I think we are realizing this. I wonder what Beagle was thinking about this system?

I do think, that if the pump is constantly flowing air due to a leak, damage could ensue.

whunter · #92 06-23-2012, 09:13 PM

Quote:

Originally Posted by kerry

So you're saying Beagle's claim is incorrect? The mechanism is always in contact with the cam so the pump is never really at rest?

If the bearing looses contact with the cam face it skips and hammers the pump to junk in short order.

Been there, seen it multiple times due to broken springs.

.

whunter · #93 06-23-2012, 09:37 PM

Vacuum Pump Rebuild Thread
http://www.peachparts.com/shopforum/diesel-discussion/229331-vacuum-pump-rebuild-thread.html#post1927867

whunter · #94 06-23-2012, 09:53 PM

Quote:

Originally Posted by vstech

yeah... I think we are realizing this. I wonder what Beagle was thinking about this system?

I do think, that if the pump is constantly flowing air due to a leak, damage could ensue.

No complaint, my best guess; he was trying to figure it out.

The prime issue is particulate intrusion effecting valve sealing, and scoring the piston cylinder.

The OM617 piston pump vents the excess air - particulate into the crankcase, not desirable in mass quantity..

This is a prime reason why I constantly recommend capping the central locking and climate control, until new owners are prepared for the diagnosis - repair.

http://www.peachparts.com/shopforum/diy-links-parts-category/142408-climate-control.html

I leave it for others to add links on central locking diagnosis - repair, as there are thousands of threads on the topic.

.

Beagle · #95 06-23-2012, 10:23 PM

Quote:

Considering how few vacuum pumps will pull 25" Hg, the claim is probably as irrelevant as it is dubious.

There seems to be a general misunderstanding of what I meant by the pump “parking itself”. The dynamics of it are really very basic school stuff. My own analysis comes from eight years as a Development Engineer in Perkins Engines R & D Test Shop and over 40 years in the F/I business, not out of the FSM or Google.

The facts are:

1) The piston is 70mmØ. That is 6in².
2) The stroke of the piston is 10mm.
3) The strength of the spring determines the level of vacuum up to what is practically achievable.

An absolute vacuum (hypothetical) would exert a forward pull of about 90lbs on the piston rod. This determines the max. strength for the spring, 90lbs to compress 10mm(length of stroke), and achieve equilibrium (i.e. park it) at a hypothetical 29.92”hg. A stronger spring would achieve nothing, just overload the mechanism and bearings and cause the pump to stroke vainly and continuously. It would be idiocy to design a pump to run continuously that is only required to work for around 5% of the time the engine is running.

A pump can be set to park at any chosen level of vacuum by adjustment of the spring strength. For example - a spring set to 45lbs to compress 10mm would park at about 15”hg. The pump starts pumping at full stroke and as the vacuum builds, the stroke progressively shortens until the vacuum pull from the piston equals 45lbs (+/-15’’hg) and equilibrium prevents the spring from pulling the piston back. There it will park and be held fully forward until vacuum falls below 15"hg allowing the spring to lower the rocker gently into the cam again. To park at 25" the spring strength is calculated to balance the vacuum "pull" at that level. It’s not rocket science!

If you drain the vacuum system, start the engine and listen with a stethoscope to the pump you should clearly hear the thump- thump of the pump on full stroke change to a tick-tick over 30 sec or so as the rocker lifts out of the cam and the roller just nicks the cam crests.

My own car still topped out at 25” recently and I am at over 2000ft here. I had changed the plate valves and bearings twice since I bought the car.

Quote:

It takes 57kg to compress the rocker to a full stroke...

This is not correct and a guess I made off the top of my head just to illustrate a point. 35kg would have been closer to the mark – Apologies.

Well that’s it folks – I’m outa here. Once again - Adios Amigos!

vstech · #96 06-23-2012, 10:34 PM

Thanks for the clarifications Beagle!!!

no matter what anybody believes, a leaking vacuum system is damaging to the pump, and not great on the engine either!

mach0415 · #97 06-23-2012, 10:47 PM

Quote:

Originally Posted by Beagle

There seems to be a general misunderstanding of what I meant by the pump “parking itself”. The dynamics of it are really very basic school stuff. My own analysis comes from eight years as a Development Engineer in Perkins Engines R & D Test Shop and over 40 years in the F/I business, not out of the FSM or Google.

The facts are:

1) The piston is 70mmØ. That is 6in².
2) The stroke of the piston is 10mm.
3) The strength of the spring determines the level of vacuum up to what is practically achievable.

An absolute vacuum (hypothetical) would exert a forward pull of about 90lbs on the piston rod. This determines the max. strength for the spring, 90lbs to compress 10mm(length of stroke), and achieve equilibrium (i.e. park it) at a hypothetical 29.92”hg. A stronger spring would achieve nothing, just overload the mechanism and bearings and cause the pump to stroke vainly and continuously. It would be idiocy to design a pump to run continuously that is only required to work for around 5% of the time the engine is running.

A pump can be set to park at any chosen level of vacuum by adjustment of the spring strength. For example - a spring set to 45lbs to compress 10mm would park at about 15”hg. The pump starts pumping at full stroke and as the vacuum builds, the stroke progressively shortens until the vacuum pull from the piston equals 45lbs (+/-15’’hg) and equilibrium prevents the spring from pulling the piston back. There it will park and be held fully forward until vacuum falls below 15"hg allowing the spring to lower the rocker gently into the cam again. To park at 25" the spring strength is calculated to balance the vacuum "pull" at that level. It’s not rocket science!

If you drain the vacuum system, start the engine and listen with a stethoscope to the pump you should clearly hear the thump- thump of the pump on full stroke change to a tick-tick over 30 sec or so as the rocker lifts out of the cam and the roller just nicks the cam crests.

My own car still topped out at 25” recently and I am at over 2000ft here. I had changed the plate valves and bearings twice since I bought the car.

This is not correct and a guess I made off the top of my head just to illustrate a point. 35kg would have been closer to the mark – Apologies.

Well that’s it folks – I’m outa here. Once again - Adios Amigos!

Thanks Beagle. That explains a lot in my mind. I see what you mean and how it works more clearly now.

funola · #98 06-24-2012, 12:53 PM

Quote:

Originally Posted by Stevo

I just tested mine using that special "t" which I made up from odds and ends, works pretty slick

Can you be more specific on what "odds and ends" you used? What did you use for the end to connect to the plastic vacuum line? Do you have a pic? What were your test results?

kerry · #99 06-24-2012, 01:04 PM

So the argument is that the piston 'floats' after it reaches a certain pressure, its stroke being substantially reduced by the effect of the vacuum on the rebound pressure of the spring?

Stevo · #**100** 06-24-2012, 01:32 PM

Quote:

Originally Posted by funola

Can you be more specific on what "odds and ends" you used? What did you use for the end to connect to the plastic vacuum line? Do you have a pic? What were your test results?

First a male and female fitting is needed (the size that fits on the brake booster) with a shot bit of hard line to slip the hose on to, (hack saw) which I got from my parts cars. Then all thats needed is finding the short piece of hose with "T" that goes in-between. I found that I couldn't use the plastic hose as it wouldn't go back over the hard line even with heat applied. The hose and "T" I found in my box of random vacuum stuff, and have no idea where it originally was from. I did take a pic of it and the hole in the pump seemingly caused by the head of the diaphragm bolt. I'll see if I can get them uploaded

The test results were just as you translated from the manual, 14 hg in 15 secs.

Stevo · #**101** 06-24-2012, 02:02 PM

Here is the hose with "T" and two shots of the hole in the pump.

funola · #**102** 06-24-2012, 05:24 PM

I have an old plastic vacuum hardline to get the male fitting from (it has 2 of them, one on each end). What I need is the female fitting such as the one on the brake booster or on the vacuum pump. Where did you get the female fitting from? Did you have to hacksaw it off? I am not near my spare piston vacuum pump or brake booster to look.

I see you have a diaphram pump with the 2 pipes. My spare vac pump has one pipe and only one fitting, which I do not want to destroy (if hacksawing is necessary).

Quote:

Originally Posted by Stevo

First a male and female fitting is needed (the size that fits on the brake booster) with a shot bit of hard line to slip the hose on to, (hack saw) which I got from my parts cars. Then all thats needed is finding the short piece of hose with "T" that goes in-between. I found that I couldn't use the plastic hose as it wouldn't go back over the hard line even with heat applied. The hose and "T" I found in my box of random vacuum stuff, and have no idea where it originally was from. I did take a pic of it and the hole in the pump seemingly caused by the head of the diaphragm bolt. I'll see if I can get them uploaded

The test results were just as you translated from the manual, 14 hg in 15 secs.

Stevo · #**103** 06-24-2012, 06:08 PM

Quote:

Originally Posted by funola

I have an old plastic vacuum hardline to get the male fitting from (it has 2 of them, one on each end). What I need is the female fitting such as the one on the brake booster or on the vacuum pump. Where did you get the female fitting from? Did you have to hacksaw it off? I am not near my spare piston vacuum pump or brake booster to look.

I see you have a diaphram pump with the 2 pipes. My spare vac pump has one pipe and only one fitting, which I do not want to destroy (if hacksawing is necessary).

Yah those female fittings are harder to find. On the later cars with the piston pump there is a short pipe coming off the VP with a male and female fitting, thats where I got the female one. I did hacksaw them off leaving as little as possible to attach the hose to. Thats because when you put the "tester" in, the black plastic line bows up with the added length and I didn't want to break it.

Your diaphragm pump has only one pipe coming off it? Huh, All the diaphragm pumps that I have seen have one to the air cleaner and the other to the brake booster.

whunter · #**104** 06-24-2012, 09:24 PM

Quote:

Originally Posted by Beagle

There seems to be a general misunderstanding of what I meant by the pump “parking itself”. The dynamics of it are really very basic school stuff. My own analysis comes from eight years as a Development Engineer in Perkins Engines R & D Test Shop and over 40 years in the F/I business, not out of the FSM or Google.

The facts are:

1) The piston is 70mmØ. That is 6in².
2) The stroke of the piston is 10mm.
3) The strength of the spring determines the level of vacuum up to what is practically achievable.

An absolute vacuum (hypothetical) would exert a forward pull of about 90lbs on the piston rod. This determines the max. strength for the spring, 90lbs to compress 10mm(length of stroke), and achieve equilibrium (i.e. park it) at a hypothetical 29.92”hg. A stronger spring would achieve nothing, just overload the mechanism and bearings and cause the pump to stroke vainly and continuously. It would be idiocy to design a pump to run continuously that is only required to work for around 5% of the time the engine is running.

A pump can be set to park at any chosen level of vacuum by adjustment of the spring strength. For example - a spring set to 45lbs to compress 10mm would park at about 15”hg. The pump starts pumping at full stroke and as the vacuum builds, the stroke progressively shortens until the vacuum pull from the piston equals 45lbs (+/-15’’hg) and equilibrium prevents the spring from pulling the piston back. There it will park and be held fully forward until vacuum falls below 15"hg allowing the spring to lower the rocker gently into the cam again. To park at 25" the spring strength is calculated to balance the vacuum "pull" at that level. It’s not rocket science!

If you drain the vacuum system, start the engine and listen with a stethoscope to the pump you should clearly hear the thump- thump of the pump on full stroke change to a tick-tick over 30 sec or so as the rocker lifts out of the cam and the roller just nicks the cam crests.

My own car still topped out at 25” recently and I am at over 2000ft here. I had changed the plate valves and bearings twice since I bought the car.

This is not correct and a guess I made off the top of my head just to illustrate a point. 35kg would have been closer to the mark – Apologies.

Well that’s it folks – I’m outa here. Once again - Adios Amigos!

I am modeling this, and will test it on an engine shortly.

On a new or low mile vacuum pump attached to a good sealed vacuum system, this sounds correct.

Sadly many systems leak, and the vacuum pump is tired.

.

funola · #**105** 06-24-2012, 10:35 PM

Quote:

Originally Posted by whunter

I am modeling this, and will test it on an engine shortly.

On a new or low mile vacuum pump attached to a good sealed vacuum system, this sounds correct.

Sadly many systems leak, and the vacuum pump is tired.

.

May I suggest:

1. Start with a brand new vac pump, ideally a piston type.

2. Drill a hole on the casing such that a borescope can be inserted, focusing on the cam and cam follower and shoot a video of the test.

Seeing is believing!