Heisler Axel Pump Design
Nelson Riedel, Nelson@NelsonsLocomotive.com
9/17/2005, last updated 09/19/2005

The Shay is equipped with a hand pump in the tender, an axel pump and a steam powered pump (an air compressor arranged to pump water).   I rarely use the hand pump and will not be equipping the Heisler with a hand pump.  I want to use the steam powered pump on the Heisler as a real air compressor for the brakes.   I also decided to provide an injector on the Heisler after seeing Dan Sharon use his injector on his shay.  The main source of feed water on the Heisler will be the axel pump described here.

The Heisler is bigger than the shay so we'll need a bit more pumping capacity.  The shay axel pump has a  0.5"  bore and a 0.625" stroke for a 0.12 cubic inch volume per stroke.  For the Heisler,  I'm shooting for about 50% increase or about 0.18 cubic inch volume per stroke. 

The axel pump on the Shay is on the middle truck.  The middle truck on the Heisler is a bit crowded with both the bevel and spur gears so the pump has to go on the front truck or the tender truck.  I decided against using the tender truck so that I could eliminate the high pressure tender-to-locomotive water line.    Only the low pressure line which will feed both the axel pump and injector will be required.

I was motivated to look at the axel pump design at this time because the gear systems had just been built and I was able to position the gears with the truck casting patterns before I sent them to Charly Wilkins.  The photo at right shows the view from the geared axel side which is the most forward axel on the front truck. The axel pump will be driven by an eccentric on the axel between the gear case and the truck side.  The photo shows there is plenty of room.   However, after fitting a model pump cylinder between the gear tube and the truck side it was determined the cylinder would work best if fitted between the gear tube and the end of the lower cross as shown on the photo.  This requires that the drive shaft be offset 0.25" from the center to give adequate clearance.  This offset will not adversely affect the drive system.
This is the view from the rear side of the front truck.  The pump will be attached to the right truck side casting.  The location of the pump cylinder is shown on the photo.
Spring loaded poppet check valves were selected for the pump valves.  The photo shows two types of check valves, both with 1/8" NPT ends.  The lower valve is McMaster-Carr #  7768K15.  I used this type valve in several places on the Shay and have been very satisfied.  The upper valve is Clippard MJCV-1AA.  I would normally use the smaller valve but was concerned about back pressure from the small passage diameter in that valve.  The passage cross section area of the Clippard valve is several times larger.  Valve outside dimensions are not an issue in this application so I chose the Clippard valve.  As a bonus, it's about half the cost of the smaller valve.	d

I also decided to use a sealed ball bearing in the pump eccentric to avoid lubrication and wear issues. 

The cylinder configuration was the last remaining design issue.   Dick McCloy (Mill Creek Central RR)  suggested that I should be able to use one of the little Clippard cylinders.  Dick uses Clippard parts in car braking systems and I used a Clippard regulator on the Shay steam atomizer feed to the burner.   I checked the Clippard website and found that several of their heavy duty Minimatic cylinders are rated for hydraulic use with a 2000 psi hydraulic pressure rating.   The cylinders are of brass and stainless steel construction with Buna N seals.  The suitable cylinders are available in  9/16" and  7/8" bore and stokes ranging from one inch  to several inches or more.    The 9/16" bore is the best match for the axel pump application except that the output port is 1/16" NPT which might restrict flow and cause excessive back pressure when pumping at high speeds.  The 7/8" bore cylinders which come with 1/8" NPT ports were then examined.  However, a 7/8" cylinder with the check valves is a very tight fit in the available space.  A second look at the 9/16" cylinders revealed that one type has a port out the back with sufficient material around the port so that it can be enlarged to 1/8" NPT.    

The Clippard H9S-1D shown above is the selected cylinder.  The drawing for many of the cylinders are available online but not for this cylinder so the drawing was made from data in a Clippard hard catalogue.  The cylinder has a stud mount on the front end which won't be used..  The cylinder is double acting with a port on each side of the piston.  Only the rear port will be used for this application; the other port will remain open.   That rear port will be enlarged to 1/8" NPT and used for the pump flow and also be used to mount the cylinder.  

Photo above shows the H9S-1D cylinder.  The cylinder was mounted in the lathe 3-jaw chuck  to enlarge the rear port.   Brass tends to grab drill bits so successive sizes of reamers were used to enlarge the hole to 11/32" and the hole was then tapped 1/8" NPT.   The end plug was unscrewed before removing the cylinder from the lathe chuck.  The cylinder and plug were carefully cleaned before reassembly.

The 9/16" bore gives 0.25 cubic inches of volume per 1" stroke.   Since we're shooting for about 0.18 cubic inches volume per stroke, we need a stoke of about 0.75"     The axel diameter is 0.875"  so the minimum  diameter of the eccentric for a 0.75" stroke is 1.625" (sum of axel diameter and eccentric throw).   The plan is to use a ball bearing between the eccentric  (inner ring) and the strap (outer ring).   Hence the minimum bearing ID is 1.625".  The nearest standard bearing ID sizes are 1.75" and  45 mm (1.772").  This is  fairly light duty and it is desirable to minimize the overall size of the eccentric so the smallest ball size and resulting smallest width and OD is desirable.   The #6809 metric bearing with 45 mm (1.772")  ID,  58 mm (2.283") OD and 7mm (0.276") width seems to be the best choice.  The 6809 has a 600 lb rated load which should be more then sufficient.    The simplest arrangement seems to be to screw the cylinder shaft directly into the eccentric outer ring and provide a swivel mount at the rear of the cylinder.. 

 With all these decisions made we're now ready for the detailed design. 

Inner Eccentric Ring:  The inner ring which holds the 45 mm ID #6809 bearing is made much wider than the 7 mm bearing width to insure stability.   Normally one would use an outside retaining ring to hold the bearing in place.  However, such a large ring is not readily available in small quantities  so instead, the retainer shown next will be used.     The inner ring will be turned from mild steel, brass or  aluminum.
Inner Bearing Retainer:  The inner bearing retainer will probably be turned with the inner ring and then parted off. The initial plan was to use socket head cap screws and leave the heads exposed.  I may change my mind and use flat head screws instead.
Outer Eccentric Ring:  The outer  ring fits over the #6809 bearing 58 mm (2.283")  OD.  The bearing will be held in place with a plate similar to that used on the inner ring.  The 3/8" diameter stub for the cylinder rod is silver soldered to the basic ring.  The outer ring will be turned from mild steel or brass.
Outer Bearing Retainer:  The  outer bearing retainer will be made of the same material as the outer ring and will be turned with the outer ring and then parted off.
Bearing Housing: The cylinder will have a swivel mount at the rear with a standard R3  bearing (3/16" ID, 1/2" OD, 13/64").   The bearing housing made of brass or mild steel shown at right will hold the bearing.  The groove is for a  1/2" shaft size inside retaining ring.
Pipe Tee: The rear port of the cylinder will be enlarged to 1/8" NPT.  The plan is to make the swivel mount by soldering the bearing housing shown above to a pipe tee that is screwed into the cylinder port. The diagram on right was downloaded from the McMaster-Carr website.  Similar diagrams are available for many of the plumbing fittings.
Pipe Street Elbow: It seems best to mount the check valves on the pump cylinder using the brass pipe 1/8" pipe street elbows shown on the right. The male tee port will screw into the tee above.  The check valves will screw into the female elbow.
Cylinder & Valve Mount: The diagram on the right shows the pump mount made from the bearing housing, pipe tee and pipe elbows.   The orientation of the elbows will position the check valves directly above and below the cylinder.  The elbows can be rotated as necessary to provide the best fit.
Mount Spacer: The spacer shown on the right will be positioned between the pump mount and the truck side. The spacer is held to the side with a 10-32 screw through the side into the spacer.  The  mount is held to the spacer with a 10-32 screw through the mount bearing into the the end of the spacer with the flats.  The spacer will be made from mild steel rod.

The drawing above shows  the top and side views of the assembled pump system.    

This drawing (above) shows the side view of the truck with the pump in position.  The pump rod is shown pushed all the way into the cylinder. The eccentric will pull the rod out as the axel turns.  The rod end of the cylinder will oscillate up and down as the axel and the eccentric turns.  The water output will be via the check valve under the cylinder since it is the higher of the two valves (the output valve should be the highest of the two so that any air bubbles are pushed out of the system).  Both the input and output water lines will connect to the pump check valves via hoses       

Drawing above shows how the the pump fits between the gear system and the truck side.   The drive shaft is 1/4" off center to give adequate clearance for the pump. 

The photo above shows all of the purchased parts (except the mount bearing that I forgot to order).  The fittings haven't been tightened.   The barb fittings will mate with 1/4" ID hose (fuel line). 

This part of the project is very interesting so I'll probably go ahead and finish the pump before loosing  interest.