LRDG Pattern condensers

[Charlie Down]

On the Chevrolet 1533X2 trucks there are 2 different types of condenser. The most common has a can with a pipe connected to the radiator and the cap on the can, that ended at the bottom of the can below the water level to condense the steam, and giving a closed pressurised system. As steam was piped to the can the pressure would increase in the can, and when the radiator cooled the positive pressure in the can would force the condensed steam back into the radiator, preventing lose of water by vented steam. Simple and straight forward to me, although I'm not sure how the pressure was controlled without a pressure relief system, or was it merely a case of keeping an eye on the temperature gauge?
However the other type has a second smaller diameter tube exiting the top of the condenser and then bending down the side of the can. I presume this was some sort of pressure relief tube. Would this pipe be below the water level in the can, in which case the pressure build up would force water out of it very quickly, or was it above the water level in which case the can wouldn't become pressurised. The third option would be for it to be above the water line but it would have a pressure relief valve on it. This pressure relief valve would have to be fitted to the smaller pipe before sealing the can up.
The first photo shows a can without the second tube, the second photo show the tube and the brackets that held it and the condenser can on the side of the truck. This doesn't appear to be a case of early and late condensers, they seem to have both been used early after the operational debut of the trucks.
So how does this system compare to later condensers on CMP trucks, and is my theory right or have I missed something?

[Tony Smith]

Both types must be vented, steam will not "Flow" into a dead-end chamber.

The Radiator Cap is a pressurised type of only around 4psi. As this opens, the pipe and condensor can (if not vented) will equally pressurise to 4psi (or higher), and nothing will flow. With nothing flowing into the Can, it cannot reduce the temperature of something that is not in it. The coolant temp (and pressure) will continue to rise unless the cooling capacity of the radiator can maintain temps. Beside the Rad Cap, there is no other means to regulate or relieve pressure in the system.

While the Condensor Can primarily condenses steam back to water by filtering it below fluid level, it also contributes to cooling the steam/liquid by being remotely mounted from the engine bay. While the Condensor Can can get warm, I've never known them to be hot to touch, or as hot as the Radiator. I've never seen steam or coolant issuing from the vents.

Originally Posted by Charlie Down

So how does this system compare to later condensers on CMP trucks,..

Both Ford and Chev CMPs had Condensors from initial production ex Factory, they are not later than the 1533. While of a differing construction, both types work on the same principle of the inlet pipe from the radiator entering the tank below a fluid level to condense any steam and/or recover liquid coolant from the radiator.

As a curiosity, I see the tanks in both your photos have a filler using the cast brass caps from 2Gal POL Cans.

[Charlie Down]

Hi Tony,
Thank you for the explanation, that all makes sense.
So there will be a vent hole in the simple condenser, maybe in the cap, and the condenser with the tube which will end below water level in the can to minimise evapouration.....
Anecdotally the drivers waited until they saw water coming from the condenser, (which is alledgedly why it was mounted in front of the driver) at which time they pointed the truck into any wind, stopped, turned the engine off, and waited for the engine/radiator to cool.
So it appears that they experienced water venting from the condenser.
That sounds like a lot of water coming from the radiator in order to fill the can, although I presume the condenser would be 1/3 or 1/2 full with water anyway to have a cooling effect. Some condensers show water staining down their sides too, suggesting venting.
Also there seems to be 2 different sizes of cans with distinctly shorter/fatter and skinny/taller cans. I haven't checked to see if the size/shape relates to the simple or vent tube designs, mostly because of the poor quality of most of the photographs.

[Hanno Spoelstra]

Are these not Chevrolet radiator overflow condenser tanks which were sold as an accessory at the time?

Ref. http://www.mapleleafup.net/forums/sh...ad.php?t=31412

[Charlie Down]

These are images of the CMP condenser and the Chevrolet civilian type that was offered as an accessory in the 1930's and 40's from a post on MLU. (Apologies I can't remember which one).
They both have lots of similar features but in different positions. The Civilian condenser has two tubes and the CMP one tube, but both on the bottom of the condenser, and both have a dome with a relief tube inside on the top.
The last photo shows another type of condenser on a LRDG Chevrolet 1311X3 from about the same time period,. The can seems to be a lighter duty version with a rolled top rim, not a welded/brazed plate.

[Hanno Spoelstra]

Originally Posted by Charlie Down

These are images of the CMP condenser and the Chevrolet civilian type that was offered as an accessory in the 1930's and 40's from a post on MLU. (Apologies I can't remember which one).

Ehm... see the link above?

[Tony Smith]

Originally Posted by Tony Smith

As a curiosity, I see the tanks in both your photos have a filler using the cast brass caps from 2Gal POL Cans.

And as distinct from the both the Chev CMP Condensor and the Ford CMP Condensor, these tanks fitted to the LRDG Trucks have a filler cap to presumably pre-fill the condensor to say 1/3 capacity to condense steam from first operation to maximise conservation of coolant.

As the inlet hose seems to go into the filler cap (from a 2Gal POL Can), and there are apparent variations in the cans, I would suggest that these are not factory made, but made in Base Workshops as a theatre modification.

[Charlie Down]

Hanno, somehow missed that link. Not very impressive considering its my posting!
Tony, I agree, the variation in can sizes and design, as well as the quality of the finish, suggests a Base Workshop fabrication.

[David Herbert]

In the last photo in post #5 I think that the pipe most likely enters the can behind the cap, not through it. If it entered through it the cap would not unscrew, particularly as the pipe is at a bit of an angle which would be an unlikely feature if it were in the cap. I think that it is just luck that the photo was taken in a way that the pipe lines up with the cap.

David

[Lynn Eades]

Charlie, here are some thoughts. Some probably slightly off topic, but cooling system related:
Water pushed from the rad. into the overflow tank stays there until the engine cools and sucks said water back into the radiator. This is achieved because that pipe into the (overflow) tank goes almost to the bottom of the tank.
Most vehicles (Tony) used early in the war did not have pressurised cooling systems, just a plain filler cap. Fords, Chevs (ref. MB-C1) Dodge and most British trucks were like this. The pressure system was adopted during the war.
Overflow tanks work with both pressure and open systems.
Thermostats were alcohol filled (bellows type) these were usually wrecked if the engine boiled. (modern wax type are much better and fail when open)
Deserts are stinking hot in the day time but usually freeze at night necessitating the use of alcohol based antifreeze. (this lowers the boiling point of water)
Although Chevs had "steam pipes", if they were producing steam, they were already in trouble.
As Tony said, all the overflow tanks had to be vented. Any negative pressure in the system would collapse the radiator as it cooled.(assuming pressure had escaped)
The downward pointing breather pipe reduces loss from the system.
The cooling systems of the era contained a larger volume (for a given power output) of water, that had a "margin of safety" that modern vehicles dont have.
The top of most radiators stood high above the top of the engine, which was a hang over from the time of no water pump. They were called a "thermosyphon" system. The water circulates from the fact that the hot water moved to the top, constantly.
The thermostat is in the system to get the best out of your engine. The longest life and best power output comes from operating inside the designed heat range. So the thermostat is there to keep your engine hot. Cooling it is another departments responsibility.
Btw, you can see by the welding at the top of the can (2nd photo) that that can is local manufacture
A modern style radiator pressure cap not only holds pressure in the system, it also has a valve to let air (or coolant) back into the system as it cools. It's the little bit in the middle.
I hope this lot helps some people.
Check out the sole of the passengers boot.