Vacuum Tank Experts please school me

[Guest Randy7]

I have two tanks and I am trying to get one to work. Both of these have a fitting on the vacuum line at the top of the tank that has a very, very small orifice built in it. I am sure this is original but it seems like the tanks pump for a little while and quit, or don't pump enough. Are these restriction fittings really necessary for pulsations or something or would the tank get more vacuum with a regular open fitting? Does anyone know the purpose for these orifice fittings? Thank you

[NTX5467]

What do these "tanks" hook to? Are they vacuum reservoirs for the hvac vacuum actuators? Or is "tank" the actuator itself?

Usually, there is a desired speed for which vacuum should be depleted from the reservoir. This can also relate to how quickly the actuator works. Much better for it to open and close gently rather than slam open due to too much vacuum flow into and out of them. The holes calibrate these things . . . so they have a reason for being there.

Enjoy!

NTX5467

[Guest MidTNDawg]

Randy7, is the orifice actually in the vacuum line from the manifold? I do not have one in mine but there is a small vent tube in the top of the tank. If the top gasket has the vent closed, i.e., not properly installed you may have that problem.

[Rusty_OToole]

Not sure what you mean by pumping. They don't really pump. Vacuum draws fuel up into the top chamber, where a float trips a valve which cuts the vacuum and allows the fuel to dump into the lower chamber.

Then the upper chamber refills itself.

The restriction is probably there to limit air flow, so the engine does not have a "vacuum leak". The flow must be calculated to allow the engine to draw enough fuel but not too much.

[Guest 1930]

I am not 100% certain of the hole you are referancing ( pics are always best ) but I believe you are describing a vacumm booster supplement. I dont even know what model vacuum tank you are referancing so again this is only a guess.

The tiny hole was added to later fittings and was said to increase vacuum 400 to 600 % and was said to be ideal when a driver was negotiating steep hills ect when there would be a lack of vacuum.

Normally located at the center of angle approach to allow entering air to increase in velocity and cause greater vacuum immidiately downstream of the orfice. It is not recomended to alter the size of the hole in any way.

Not sure what you mean by open fitting either, the term open does not sit well with me, you need vacuum so nothing can be clear and un obstructed open.

Edited September 18, 2011 by 1930 (see edit history)

[Guest 1930]

Quote....the tank pumps for a little while and then quits...........Again more specific info would be needed to help further I.E. what type of tank make and model of car might prove usefull, pictures of the plumbing might cinch it.

[Guest Randy7]

Ok I'll try to be more clear. I am talking about the Stewart vacuum fuel canister on a 1919 dodge. It holds fuel that is sucked from the gas tank by vacuum before going to the carburetor. On the top plate of the Stewart canister there are threaded openings for vent, gas in, vacuum suction and a fill plug.

The suction or vacuum line from the engine intake manifold is a quarter inch copper line with a 90 degree elbow screwed into the correct threaded opening in the Stewart top plate. This 90 degree elbow has in the end that screws into the plate a solid ID section in the threaded end and it reduces the ID to a very small hole (orifice) . This small hole restricts the 1/4 inch ID of the fitting. This metering hole is smaller than a 1/16 of an inch. It is not your normal 1/4 inch pipe fitting that has a 1/4 inch inside diameter clear through it. With that small orifice in the vacuum line from the engine I would think it would really reduce the amount and recovery time of vacuum the engine would pull on the stewart tank. I don't see how it could possibly increase vacuum. I was considering changing it to a regular 1/4 inch ID elbow to get a larger ID to possibly get more and faster vacuum recovery in the Stewart canister? Sorry for the confusion.

[hddennis]

Randy7, try here and see if this helps you:

http://hudsonterraplane.com/tech/1927/StewartWarnerVacuumTank2-11-27.pdf

http://old-carburetors.com/1927-Dykes/1927-Dykes-072.htm

Howard Dennis

[Guest Randy7]

Thank you Howard for those two manuals. They definitely show it, it's the "W" restrictor fittiing drill size #37 in the diagram. I don't know why they would restrict the vacuum line so much but they built it so I am not going to question them, I will put it back in. After seeing that manual I am suspicious that my atmosphere tube at the gasket flange is plugged. That gives me something to go on. Thank you !

[hddennis]

Glad to help.

Howard Dennis

[1936 D2]

I like this quote, right out of the Stewart-Warner Installation & Care Manual:

"CARE OF THE STEWART-WARNER VACUUM TANK

No care whatever is required of the tank and it is quite

unlikely that you will ever have to touch it because of any

imperfect functioning of the tank."

[Guest cben09]

The small restriction hole is there so that it wont lean out the mixture and have the engine stall when it goes to syphon mode,,,

Usually the idle is fast enough so this not a problem,,,really not that fussy,,but with that Stewart carb,,,the idle was legendary,,Have fun,,Ben