Diesel HAC (1 Viewer)

[heilanpiper]

Anyone here owns a 3B with High Altitude Compensator? It has become unavailable unless someone sells one. I need some specifications that could allow me to recreate them.

Whoever here has one on your truck, please do the following for me:-
1) measure the protruding portion of your HAC and give me your approximate elevation. Vernier Caliper should suffice; no need for dial gauge.
2) if you are able to hook your free ended hose to a hand mightyVac pump, record the protrusion change. Make a table at 1”/mg interval. Every inch of mercury corresponds to 1000 feet of elevation.

I need to know how much it moves per 1000 feet and I can work backwards and build an appropriate aneroid capsule.

 

[AussieHJCruza]

A turbo is a sort of HAC...

 

[heilanpiper]

A turbo is a sort of HAC...

You are correct. Turbo compensates But when I am around 7,000 feet to 11,000 feet, I am coal rolling and is not a problem as I do not live there and can do a simple adjustment to compensate. I can build and design a HAC if I knew the Specifications of the original HAC.

Maybe I am being pedantic but here in Canada and USA, we have crazy high mountain roads. Definitely not an issue down under.

 

[roalco]

Hi, the DHAC unfortunately cannot be tested that way, as the internal aneroid bellows are sealed from the factory and the ambient air pipe is common to the interior of the housing (they could have just drilled a hole in the housing, but the whole reason for the semi sealed housing, boot, and inlet hose is to keep moisture and debris out). And the housing is only dustproof and will not maintain a vacuum. You would need to rig up a dial indicator on the actuator end, then put the whole thing in a vacuum pot. Or simply take a detached one on a mountain drive, with an altimeter, and measure the actuator protrusion at various elevations.
Heilanpiper, I sent you a PM.

 

[heilanpiper]

Hi, the DHAC unfortunately cannot be tested that way, as the internal aneroid bellows are sealed from the factory and the ambient air pipe is common to the interior of the housing (they could have just drilled a hole in the housing, but the whole reason for the semi sealed housing, boot, and inlet hose is to keep moisture and debris out). And the housing is only dustproof and will not maintain a vacuum. You would need to rig up a dial indicator on the actuator end, then put the whole thing in a vacuum pot. Or simply take a detached one on a mountain drive, with an altimeter, and measure the actuator protrusion at various elevations.
Heilanpiper, I sent you a PM.

I create a reduction in baro by applying a controlled vacuum to the hosed port and that will allow the aneroid capsule to extend. My testing will be non destructive and non intrusive. I know what is inside the DHAC already, just need to match up the performance characteristics with off the shelf capsules, possibly stacking them to get the desired compensation.

 

[heilanpiper]

I read the engine manual and found the table for the Diesel HAC outlining the amount of movement. From what I read, it retracts on higher altitude (need to confirm that). The capsule moves 0.75mm per 1000M of elevation to a max of 3.1 to 3.6mm. If it retracts on higher elevation, the aneroid capsule internals are exposed to Baro, while encased in an outer shell calibrated at Zero MSL; conversely if it extends, then the aneroid capsule is sealed at Zero MSL and the housing is exposed to Baro.

I think I will still need to have a closer look at a running set up to see what it moves, and copy the bracket as well.

 

[roalco]

Exactly! The aneroid internals are sealed at sea level (zero msw) pressure so that the push rod extends at increasing altitude, and acts as a modified fuel stop (on a different actuator lever than fitted to the standard governor). As the housing is only dust and moisture proof (ie. it leaks) a continuous vacuum must be applied to test, a hand vacuum pump will not keep up with the normal housing leakage volume.

 

[roalco]

Here’s a couple of pictures, of a DHAC both assembled, and disassembled. As you can see, the aneroid capsules threaded attachment/adjustment post has an axial bore to allow ambient air from the collection tube to be routed to the inside of the housing by a radial bore at its base. It does not enter the aneroid capsules, which are sealed. The actuator shaft, under the rubber boot, has not been removed, but has an free sliding fit to reduce friction (which allows air leakage to and from the housing). The actuator shaft is retained by a circlip, which allows a maximum of 5mm travel.
there is no seal between the housing body and lid, just two edge stampings to lock it in place. The copper washers, and both the locknut and nipple (with lock wire drilling’s) are used to prevent any change in adjustment once sea level pressure clearance has been set, by turning the end of the aneroid capsules post with a straight bladed screwdriver (under the nipple).

 

[roalco]

Oh, and here’s a terrible shot of a picture of a DHAC installed on a B class engine, showing the different actuator arm and EDIC linkage. Apparently the EDIC linkage arms are the same, so there is no change needed.

 

[heilanpiper]

Thank for the lovely information and pictures. Can you give me the diameter of the aneroid capsule, and the stacked height? From what you have given me, we can reverse engineer the D-HAC and I can begin matching up a suitable aneroid capsule.

I have sent of an RFQ to the aneroid capsule supplier, to meet the same performance specification. I would design it slightly differently. I would put the sense port on the housing directly and not use a threaded nipple and hollow threaded pipe and opt for a solid post instead.

Loving the combined brain trust here on mud. Very glad I joined and should have joined a decade ago.

 

[roalco]

The outer diameter of the 3 element aneroid unit is 1.980”,
The core pieces are 0.592” in diameter,
The length of the aneroid element is .745”, with approximately .100” of compression until solid.
(length taken today in north Vancouver at approx. , 230‘ (72m) elevation, 101.77kpa, 11C)

 

[heilanpiper]

The outer diameter of the 3 element aneroid unit is 1.980”,
The core pieces are 0.592” in diameter,
The length of the aneroid element is .745”, with approximately .100” of compression until solid.
(length taken today in north Vancouver at approx. , 230‘ (72m) elevation, 101.77kpa, 11C)

Thank you for more solid information.

 

[roalco]

You’re welcome!