VanBrocklin style duplex pump

[PeterCraymer]

I have decided to add another method of adding water to the boiler by building a duplex pump. They are neat to watch operate as they never get out of time from the other cylinder becasue the valve from one cylinder operates the other. Quite genius. My machining skills pale in comparison to others that post here, but feel free to comment and offer suggestions. I will start with a few photos. Don't fret over the marks and holes not lining up. The marks were only made for reference and the actual positions were determined by indicating on the mill!

Peter

[SteveM]

This will be great to have a build on this documented.

What scale is that?

Steve

[Bill Shields]

it is one of my 1-1/2" variants of the original VB pump, and he appears to be doing a very nice job.

[PeterCraymer]

Sorry for lack of progress here. That job and family stuff comes 1st. Here is a link to a video of the steam end operating on air. The water end has nothing other than a few ports so that it won't lock up on compression. Still to be done is all the ports and check valve seats in the water end, make gaskets for all the heads, and clean up machining marks after final countouring on the outside of the cylinders on the rotary table. (It is much easier to setup rectangles to machine on the mill than 1/2 round objects and won't leave flat spots either)

http://www.youtube.com/watch?v=ykghaeH7 ... 082dqbLJDQ

(not sure how to embed the video)

The steam ports were challenging, but not to the point of frustrating. The only real issue so far has been that the thread on the steam pistons wasn't 100% straight and on initial installation, the piston was scrubbing the cylinder wall at the end of the stroke. A couple of thou off of the OD (didn't change the o-ring backer) and she runs smooth. It will tighen up some once all the packing o-rings are in the steam chest, but nothing to fret over. I will try to take more photos when I take it apart for more machining.

Steve, not sure if I answered before, but this is 1.5" scale. It is for my Allen 10-Wheeler.

Peter

[Bill Shields]

looking good.

I find that sometimes a 'pilot bore' in the piston to center the rod irrespective of the thread clearance helps.

[Hudson Honey]

very nice indeed.

with the Worthington pump...you really see nothing moving other than the support shaft David M. added coming out of the head and of course the chug chug sound it makes.

it's always neat to see all the levers and rods moving. adds a lot of interest.


Pamela

[PeterCraymer]

I found a couple of pictures that will now be out of order, but may be interesting anyway! They show the in process part of making the spacer spools, cylinder head stock (turned hex from a previous job) and the plugging of the extra holes required to make the steam ports intersect. I used 12 or 14 gauge Romex (don't remember which - point was it was solid copper and cheap and easy to manipulate) with a press fit (well needlenose and a hammer!) into a slightly chamfered/countersunk hole for the silver solder. The press fit kept any material from heading down the ports and silver soldering made it steam worthy related to temperature. I pre-heated the entire block and then turned each face up to do the final solder on that face so that it would fill most of the chamfer/countersink. Not really necessary, but it made me feel better about knowing it was properly sealed and filled up. Looking at the pictures where the steam cylinders are standing on the not yet slotted spool spacers, you can see the copper bits and the silver solder fillets filed smooth on the top face. Currently this thing with the water end on it weighs 3 or 4 pounds!

[PeterCraymer]

Bill,

In regards to the piston, next time I will probably just do the finished machine work once the piston is permanently attached to the piston rod. I really am not sure why it was so crooked. When I say crooked, it may have been .010 or .015 that the face wobbled, so not too bad. The water pistons were dead on! I machined all the pistons in the same setup including the drilling and threading of the bore. My guess without dissassembly is that the thread (done with a die) on the end of the piston rod is the culprit! It doesnt take much to get that off with threads that small. My home lathe isn't setup to thread with a cutter on the toolpost yet, so I still have to use a die and holder. Usually the results are accurate enough, but in this case, the clearances (cumulative or singular) are close enough that any small angular mis-alignment can cause a problem.

Peter

[Bill Shields]

yes, that can cause the problem.

I usually single point thread the rods in the lathe first, then run a tailstock held die over them to clean the threads up.

another way would be to drill / tap the piston rod and put in a socket head cap screw from the piston down in.

either way will get you where you are going...and you are well on your way!

[Mike Walsh]

Can this pump air? If so, could this be a reliable design for an air brake system?

Mike

[Bill Shields]

no....

[steamingdon]

Steve M.

You should look around your own club PVLS, most of your pump questions can be answered. This is far from the first build article on Van Brocklin pumps. Bill & I have both written and took photos of these projects. It is nice to see someone else take a crack at building one of these, they can be tricky.

Don