Vacuum Tank Questions

[Flivver guy]

I am waking up my Packard after a long slumber. I took apart the vacuum tank and cleaned out all the crud. Cleaned up the float mechanism and thought all was good. I reassembled the tank and poured some gas into the can. I started the car, but it will only run if the plug on top of the can is removed. With the plug in place the vacuum builds but it stalls the motor. With the plug off, it will run fine, but isn’t pulling any fuel from the tank.

 

Thoughts??

[Flivverking]

Is the top vent port clear? 

[Flivver guy]

I will check thanks.

[wayne sheldon]

Vacuum tanks are a marvel of Rube Goldberg engineering, that add a special dimension to the antique automobile experience. Once working properly, they usually become very reliable (except for those sometimes long steep climbs that allow them to run out due to too low an engine vacuum pressure). If you drive one enough (which everybody should!), that is easy enough to deal with (just knowing about when to pull over and give the car a minute or two break to refill the tank at idle).

 

There are a couple double ended valves that need to switch in unison between simple draining from the tank into the carburetor, and the tank sucking fuel from the gasoline tank. Generally, it is not wise to take the assembly completely apart (although sometimes it might be necessary?), and usually, if they are in decent condition, they do not need such extensive work done to them.

There are two things that are critical to their operation. One is the vacuum integrity, both between the chambers, and to the outside air. The other is venting. 

There are two chambers, the upper chamber that takes the intake vacuum from the engine and with the valves switched properly will draw fuel from the gasoline tank. And the lower chamber which holds the ready fuel to drain into the carburetor. 

THERE MUST NOT BE ANY LEAKAGE BETWEEN THE TWO CHAMBERS! And that includes the simple flapper valve at the bottom of the upper chamber, which sometimes with age may have become warped or corroded (often an easy fix). And there must be no leakage around the gaskets between the top piece and the chambers.

There is a small vent on the outer edge of the top of the lower chamber that feeds into the top valve mechanism. Make sure that passageway is clear. 

The valve mechanism in addition to switching the vacuum into the upper chamber, switches the venting around. There should be a short small tubing in a fitting in the top piece. This is the main vent. 

Rig up a piece of clean tubing onto the vacuum line that should connect to the intake manifold. Then, while sucking onto the tubing (hence clean?), Move the float up and down. You should be able to know almost instantly whether the valves are working or not. You should with a little effort be able to tell if the venting is switching to the lower chamber or not.

Venting into the upper chamber MUST shut off completely for the vacuum to pull fuel from the gasoline tank. And it must vent in order for the upper chamber to properly drain into the lower chamber.

 

Been awhile since I worked on one. IF I recall correctly, the lower chamber should vent though the upper chamber when the upper chamber is not pulling from the gasoline tank. But the lower chamber MUST vent around the upper chamber while the vacuum is switched to pulling fuel, otherwise the engine would soon stall because the fuel couldn't properly drain to the carburetor without any venting.

 

As I said. Once sorted out and working properly, the vacuum tank experience is a good one. You will find that if everything is set up and running well, whether driving or sitting and idling, every so often, the idle will vary a bit, with a slight stumble for just a couple seconds. That is the shifting of the vacuum which alters the fuel to air mixture very slightly. It tells you that all is well (at least that much of it?).

[Grimy]

Ensure that the vent hole in the lid matches the vent hole in the body and is not occluded by the gasket(s).

 

As @wayne sheldon said, the two valves (suction and atmospheric) in the lid must operate sharply--when one is open, the other must be closed.  I've found "whiskery" corrosion on the valves themselves and on the pivot pins which has the effect of degrading the valves' opening and closing action; this corrosion can be easily removed with carb cleaner and a *nylon* brush.  Also, the valve seats inserted into the pot metal lid can come loose, and if so can be *gently* staked.

[DFeeney]

In the general discussion of Vacuum tanks please note that the 28/29/30 MoPar Plymouths received their Vacuum from a orifice  in the oil pump.

[wayne sheldon]

It should be mentioned here for the clarification for others reading this, that the vacuum tank of which we are discussing is the fairly common type Stewart Warner vacuum tank (fuel pump) in use on hundreds of marques from about 1914 until about 1930. I/we knew this because Flivver guy a couple days ago shared a few pictures of his new car! In one of the photos showing the engine, the vacuum tank can barely be seen. In the case of this and many Packard automobiles of the mid 1920s, the vacuum tank is a considerably larger outer tank than most Stewart Warner tanks used. However, the top and mechanism is basically the same on most Stewart Warner tanks from the beginning until the late 1920s regardless of tank size. 

Besides, some of us (including Grimy I am sure!) have looked at enough Packards to know they used the Stewart Warner vacuum tank. There are many variations, sizes and capacities of outer and inner chambers/tanks, minor model differences, different identification tags, different sizes and types of inlet fittings etc etc etc. However, mechanically, most of these S/W tanks are basically the same.

There were a couple other companies that manufactured vacuum fuel pumps during those years, both in the USA and other countries. All of those are generally very different mechanically and operation than the common S/W tanks. And Stewart Warner did also manufacture a different series of tanks in the late 1920s and early 1930s which were used by several automobile manufacturers including several Chrysler products. Those are also very different from the common S/W tanks used for more than fifteen years.

[hchris]

11 hours ago, wayne sheldon said:

Vacuum tanks are a marvel of Rube Goldberg engineering, that add a special dimension to the antique automobile experience. Once working properly, they usually become very reliable (except for those sometimes long steep climbs that allow them to run out due to too low an engine vacuum pressure). If you drive one enough (which everybody should!), that is easy enough to deal with (just knowing about when to pull over and give the car a minute or two break to refill the tank at idle).

 

There are a couple double ended valves that need to switch in unison between simple draining from the tank into the carburetor, and the tank sucking fuel from the gasoline tank. Generally, it is not wise to take the assembly completely apart (although sometimes it might be necessary?), and usually, if they are in decent condition, they do not need such extensive work done to them.

There are two things that are critical to their operation. One is the vacuum integrity, both between the chambers, and to the outside air. The other is venting. 

There are two chambers, the upper chamber that takes the intake vacuum from the engine and with the valves switched properly will draw fuel from the gasoline tank. And the lower chamber which holds the ready fuel to drain into the carburetor. 

THERE MUST NOT BE ANY LEAKAGE BETWEEN THE TWO CHAMBERS! And that includes the simple flapper valve at the bottom of the upper chamber, which sometimes with age may have become warped or corroded (often an easy fix). And there must be no leakage around the gaskets between the top piece and the chambers.

There is a small vent on the outer edge of the top of the lower chamber that feeds into the top valve mechanism. Make sure that passageway is clear. 

The valve mechanism in addition to switching the vacuum into the upper chamber, switches the venting around. There should be a short small tubing in a fitting in the top piece. This is the main vent. 

Rig up a piece of clean tubing onto the vacuum line that should connect to the intake manifold. Then, while sucking onto the tubing (hence clean?), Move the float up and down. You should be able to know almost instantly whether the valves are working or not. You should with a little effort be able to tell if the venting is switching to the lower chamber or not.

Venting into the upper chamber MUST shut off completely for the vacuum to pull fuel from the gasoline tank. And it must vent in order for the upper chamber to properly drain into the lower chamber.

 

Been awhile since I worked on one. IF I recall correctly, the lower chamber should vent though the upper chamber when the upper chamber is not pulling from the gasoline tank. But the lower chamber MUST vent around the upper chamber while the vacuum is switched to pulling fuel, otherwise the engine would soon stall because the fuel couldn't properly drain to the carburetor without any venting.

 

As I said. Once sorted out and working properly, the vacuum tank experience is a good one. You will find that if everything is set up and running well, whether driving or sitting and idling, every so often, the idle will vary a bit, with a slight stumble for just a couple seconds. That is the shifting of the vacuum which alters the fuel to air mixture very slightly. It tells you that all is well (at least that much of it?).

Along with the slight idle stumble, you can feel a drop in temperature if you hold the vac tank fuel input pipe, this is another indicator that  fuel is flowing through it.

Edited March 27, 2022 by hchris
Words (see edit history)

[Grimy]

9 hours ago, wayne sheldon said:

It should be mentioned here for the clarification for others reading this, that the vacuum tank of which we are discussing is the fairly common type Stewart Warner vacuum tank (fuel pump) in use on hundreds of marques from about 1914 until about 1930. I/we knew this because Flivver guy a couple days ago shared a few pictures of his new car! In one of the photos showing the engine, the vacuum tank can barely be seen. In the case of this and many Packard automobiles of the mid 1920s, the vacuum tank is a considerably larger outer tank than most Stewart Warner tanks used. However, the top and mechanism is basically the same on most Stewart Warner tanks from the beginning until the late 1920s regardless of tank size. 

Besides, some of us (including Grimy I am sure!) have looked at enough Packards to know they used the Stewart Warner vacuum tank. There are many variations, sizes and capacities of outer and inner chambers/tanks, minor model differences, different identification tags, different sizes and types of inlet fittings etc etc etc. However, mechanically, most of these S/W tanks are basically the same.

There were a couple other companies that manufactured vacuum fuel pumps during those years, both in the USA and other countries. All of those are generally very different mechanically and operation than the common S/W tanks. And Stewart Warner did also manufacture a different series of tanks in the late 1920s and early 1930s which were used by several automobile manufacturers including several Chrysler products. Those are also very different from the common S/W tanks used for more than fifteen years.

Thanks, Wayne.  Yes, I know that these Packards use the S-W vac tank.  Over the years I picked up a few tanks with different-sized reservoirs but all with the common 4.25-inch OD cover.  Since the cover itself is pot metal, it's good to have a spare.  And a word of caution:  because of the pot metal material, do NOT tighten anything excessively!  If judging points are not an issue, spread the load by placing a flat washer under each machine screw fastening the the cover to the reservoir.  As mentioned above, double check the alignment of the cover to the reservoir to ensure that you are not covering the essential-to-operation vent hole.

[Flivver guy]

Do I have an issue with the way these rivets are attached? Almost looks like there should be a spacer in there to me.

[HarryLime]

No , that is normal . That is the flapper hinge .

[Flivver guy]

Well it seems that I have successfully gotten my vacuum tank functioning properly. The car seems to run great! There is a slight hesitation in the carb. I will rebuild that next. Along with installing a new wiring harness.

Thanks for all of your guidance.

[wayne sheldon]

Nice! It is wonderful to hear an antique automobile running for the first time in many years. Especially if it wakes up and runs great!

[Dandy Dave]

You already got great advice here. Vacuum Tanks are a fairly simple device. But, Everything need to be right for them to function correctly. Please share some photos of your car. We like pictures. Especially of autos that have sat for years and are resurrected. I've used the vacuum tank on my 1915 Buick for years. It is a very reliable system. Dandy Dave! 

[hook]

Maybe this will help.

[Flivver guy]

Thanks Hook. I will save these.

[Stude Light]

While diagnosing my fuel pump I attached a vacuum gauge to the fill plug. It helped to verify when it was cycling. It's interesting just how often they do cycle.

Scott

[m-mman]

 

 

These are two videos from when I was learning the operation of a vacuum tank on my 1929 Cadillac. 

It gauge is connected to the "fill/priming" hole in the center of the lid as shown by Stude Light above.

 

You will see no vacuum because the engine is running on fuel flowing by gravity from the outer tank into the carb.

Then when the inner tank runs low, the float falls (vacuum shows on the gauge) while fuel is being drawn from the tank. It doesn't take much to fill the inner tank and when full, the vacuum shuts off. 

Edited April 1, 2022 by m-mman (see edit history)