3/4" Scale Van Brocklin Duplex Pumps for sale ****SOLD****

[Leeadamaa]

Hey All,

I am selling my recently completed batch of steam pumps I have yet to confirm the shipping price but would assume it will not be cheaper than 40$ so you can add 40$ to the price of the pump.

I will post video of them running on air and pumping water they tick over on almost a whisp maybe less than 5PSI

I've been working on these since February lots and lots of hours.

Prices 600$USD and approx 40$ for shipping to be confirmed at a later date

PM Me if you're interested.

[backyardrails]

What type of o-ring did you put inside?
Bernie

[Leeadamaa]

5/8" Viton for the Steam Side
10MM OD Rubber for the Water Side

[Leeadamaa]

I have 1 Pump not spoken for yet.

[Leeadamaa]

All Pumps gone.

[Wolfgang]

Sorry to rain on your parade, but the pumps shown above are not duplex pumps.

With the valve actuators as shown you have in effect 2 simplex pumps stoking alternately.

On a true duplex pump the strokes overlap, ideally by 50% but this can be difficult to achieve.

[Harold_V]

Wolfgang,
If I understand duplex pumps, they have a low pressure cylinder and a high pressure cylinder. Discharge from the low pressure cylinder is fed to the high pressure cylinder, raising the overall pressure. For that reason, the cylinders are out of phase with one another by approximately 180°. Is that correct?

H

[Steve Bratina]

All the "duplex pumps" that I ever worked on or rebuilt were operated, as these pumps are, with the valve on the left side operating the steam piston on the right side and vice versa. The one side almost completes its stroke before the other side begins to move. To because there is no dead centre, the pump will restart where ever it stops. Both valves require a loose fit on the valve rod to work properly and not short stroke.
Simplex pumps have one pump, duplexes have two. Compounds are a different thing all together. What Steven has here are duplex pumps.
Hey Wolfgang. Where is that Hudson hiding?

[Wolfgang]

Wolfgang,
If I understand duplex pumps, they have a low pressure cylinder and a high pressure cylinder. Discharge from the low pressure cylinder is fed to the high pressure cylinder, raising the overall pressure. For that reason, the cylinders are out of phase with one another by approximately 180°. Is that correct?

H

Harold,

What you are describing is a compound cylinder arrangement whereby the exhaust steam from the small cylinder (receiving steam directly from the boiler) is admitted to the large bore cylinder for additional expansion (and work).

Properly executed and operated this cylinder arrangement and steam utilization improves the overall efficiency by a large measure. Think seriously reduced fuel consumption.

Duplex pumps typically have both cylinders the same diameter.

Using crank angle analogy, the cylinders on a duplex pump would ideally operate at a 90 deg. crank angle which, as I stated earlier, is very difficult if not impossible to achieve in practice because there is no mechanical linkage connecting the two cylinders or their valves to keep things synchronized.

However, the piston on one side must operate the valve for the other cylinder or the thing won't run; there is additional complication that one cylinder must have crossed steam passages or the thing won't run.

In practice this crossing of the passages may be achieved in one of two ways:
1) external valve linkage consisting of a first class lever for one side, and a second class lever for the other side.
2) the passages may be crossed internally in the cylinder block, in which case only first class levers are required externally. This is how I did it with my design.

These levers are necessary in order to time the valve operation such that the second valve is opened when the first cylinder has completed only part of its stroke, thus creating the overlapping of the strokes of the 2 cylinders thus increasing volume flow improvement and efficiency. In other words, by proportioning the levers and adding a small amount of lost motion between the lever clevis and the valve rod actuating spool that engages the lever clevis, one tries to achieve this stroke overlap or 90 deg. phase angle in crank analogy.

Unfortunately with the model shown above these levers are missing and without them one has two simplex pumps stroking alternately, ie one cylinder completes its stroke (or very nearly so) before the other cylinder begins its stroke. In a true duplex pump the second cylinder begins its stroke when the first cylinder has completed only one half of its stroke (or a little less).

I designed and built 3 duplex pumps that were described in Model Engineer Magazine back in 1995, utilizing the lever action as I described herein. It adds to the complexity of the model as there are a number of finicky parts to machine and fabricate. But they are beautiful mechanisms to watch when operating.

Anyone interested, I have full drawing sets available, including assembly drawings and full material bill, for U$75, air mailed anywhere... But there are finicky parts as I said. Over the years I have sold sets of drawings all over the world, and saw one that was built to my plans at the Hamilton Steam Museum, in operation.

[Wolfgang]

All the "duplex pumps" that I ever worked on or rebuilt were operated, as these pumps are, with the valve on the left side operating the steam piston on the right side and vice versa. The one side almost completes its stroke before the other side begins to move. To because there is no dead centre, the pump will restart where ever it stops. Both valves require a loose fit on the valve rod to work properly and not short stroke.
Simplex pumps have one pump, duplexes have two. Compounds are a different thing all together. What Steven has here are duplex pumps.
Hey Wolfgang. Where is that Hudson hiding?

inter

Hi Steve!

Long time no see.

The Hudson 2888 is in the shop awaiting overhaul. The oil pump check valves have been problematic, and the hand pump is seized. Don't know what else ails it. It hasn't been steamed since 2012 or so; many life changes came in the way. Hope to overhaul it this coming winter.

[Harold_V]

Thanks, Wolfgang. You helped clear up some misconceptions I had about those pumps.

H

[Carrdo]

Wolfgang's duplex pumps are truly beautiful and so are his drawings.

I just haven't built up the courage to start on one yet.