We've covered the entire design expect for the valves
in Parts I, II & III. Can't put it off any longer --- time to do
the valves.
The prototype uses piston valves with cast iron rings for both the main valve
and the reversing valve. A
whole bunch of rings are required and I wasn't excited about making the
rings. One alternative is to use slide valves but they have their
own set of problems such as not sealing very well and it's difficult to
get at the sealing surfaces. Personal experience has shown that O-Rings
work great on main pistons but I didn't think they would work on valve pistons
where the side of the rings have to slide over the ports in the side of
the cylinder. I did a little research on this before
starting the compressor design and found that O-Rings seem to hold up
on valve pistons. One possible reason is that the pressure in this
application is much less than in many other O-Ring applications so the
O-Ring squeeze can be less. The test results are at
Using O-Rings on
Piston Valves. I also found one manufacturer that uses
O-Rings on the valve piston of a steam powered pump.
One of the challenges with the valve design is to
figure out how to route the the steam from the ports to the destination
indicated on the drawing. Turns out that it isn't as bad as
it looked initially.
Another decision is the diameter of the steam passages. I used
3/32" diameter passages on the single cylinder water pump on
the shay. It was capable of running much faster than desired when
the supply valve was completely opened. I decided to make
the majority of the passages here 0.089" with any open ends plugged
with 4-40 set screws. The ends of the exhaust and steam
input passages are 1/8" with the open ends plugged with 6-32 set
screws.
Valve Assembly: The drawing on right
identifies the parts which comprise the valve
assembly. Drawings for individual parts are below. The individual parts are:
- HM562-Upper Steam Cylinder Head
- HM563 - Valve Housing
- HM564 - Valve Reinforcement
- HM565 - Reversing Valve Piston
- HM566 - Reversing Valve Cover
- HM567 - Main Valve Sleeve
- HM568 - Main Valve Piston
- HM569 - Main Valve End Covers
- HM570 - Upper Steam Head Large Alignment Washer
- HM570 - Upper Steam Head Small Alignment Washer
- HM572 - Reversing Valve Rod.
|
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| Upper Steam Cylinder Head: The outside edge
and attachment bolt pattern of the upper steam head is identical to
that of the other three heads. The upper steam head is
different in that it is machined from 5/16" thick stock.
The 0.906" wide center section is 5/16" thick while the
rest
of the head is milled down to 1/8" thickness matching the other heads.
The input & exhaust passages run through the thicker middle
section, the exhaust on the left and the steam input on the right.
|
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| Upper Steam Head Passage Dimensions:
The Upper Steam Head drawing is repeated on the right with the
attachment holes removed so that the position of the passages can be
dimensioned more clearly The vertical holes on each end match
up with passages down the side of the cylinders to the steam
input and exhaust ports. The other vertical holes match
up with mating holes in the valve housing which sets on the head. |
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| Valve Housing: The
valve housing is made from a 3/4" length of 2" diameter brass or
bronze. The sides are milled to the dimensions shown.
The 0.906" section lines up with the raised part of the upper steam
head. The vertical 3/8" diameter hole is the reversing valve
cylinder. The 9/16" horizontal hole will hold the main valve
sleeve. The 3/8" wide recess in the left side is for the
Valve reinforcement.
Many additional holes are required for the valve passages.
These passages are shown in subsequent drawings.
|
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| Valve Reinforcement: This piece
reinforces the upper part of the compressor so that it can be
hoisted by the eye. This piece has no function on our
model other than aesthetics. |
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| Valve Housing & Reinforcement
Attachment: The valve housing and reinforcement are each
attached to the head with two 7/16" long #2-56 FH brass screws up through the
head. The drawing shows the approximate position of these
screws. The exact position is not critical except the screws must
miss the steam and exhaust passages that run side-to-side through
the head and also miss the other steam passages that run through the
valve housing. The holes in the reinforcement and housing
should be tapped about 3/16" deep.
The housing and reinforcement will be silver soldered to the
head. These screws will hold everything together during the
soldering process and also keep everything is position should the assembly be reheated
later.
|
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| Valve Output Passages: There are
four valve output passages, one to each end of each steam cylinder.
The passages go down through the valve housing and through the head
via 0.089" holes that are tapped 4-40 on the under side of the head.
(The threaded ends are plugged with setscrews during testing
of the
valve system.) The slots provide access from the passages to the
top of the two steam cylinders. The other two passages feed
through mating holes in the steam cylinder unit (through the filler
strip between the cylinders) to the bottom of the cylinder and then
out through similar slots in the bottom of the cylinder unit to the
bottom of the two steam cylinders. |
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| Valve Exhaust Passages: The
drawing shows the exhaust passages. The main exhaust passage
runs across the head from the left side. The left end of
the passage is plugged with a 6-32 setscrew. The passage
connects to the exhaust port via a passage down the side of the
cylinder. The passage connects to the center of the main valve
via the hole up through the head. The lower end of that hole is
plugged with a 4-40 setscrew. The right end of the
horizontal passage opens into the area around the reversing valve stem and in
turn to the bottom of the reversing valve cylinder. The 1/16"
vertical hole connects from the horizontal exhaust passage to the
top of the reversing valve cylinder. The slot between
the hole and the top of the cylinder as well as the top of the hole
are covered
by the reversing valve cap. |
 |
| Valve Steam Passages: The steam
enters via the port on the right side of the high pressure steam
cylinder, travels up the side of the cylinder and into the
horizontal steam passage in the right side center of the head.
There is a vertical passage up the right side of the valve housing that
intersects with the horizontal passage in the head. A
horizontal passage in the valve housing to the right of
the reversing valve cylinder intersects with the vertical passage
and provides steam to the center of the reversing valve. All the
remaining passages are horizontal in the valve housing. One
passage runs back to front on the right end of the housing
interesting the vertical passage. This passage
intersects a passage that runs right to left in front of the
reversing valve and intersects a passage that runs back to front
along the right side of the main valve cylinder. There are intersecting
passages on this back-to-front passage that carry the steam to the
main valve cylinder. |
 |
| Valve Inter Cylinder Passages:
The inter cylinder passages carry the steam that operates the main
valve. One path travels horizontally right to left behind the
reversing valve where it intersects a back to front path that goes
into the reversing valve cylinder. A second back to front
passage is at an angle along the side of the main cylinder and also
intersects the left to right passage. This second back to
front passage carries steam to the rear end of the main valve
cylinder. There is a similar set of passages along the front
of the valve housing that provide steam to the front of the main
valve. |
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| Reversing Valve Piston: The
reversing valve piston will be turned from 3/8" brass rod.
Care should be taken to make the grooves as accurate as possible.
The piston threads onto the end of the valve rod. |
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| Reversing Valve Cap: The cap is
made from 3/4" square brass bar. The cap can be used as a
template to drill and tap the four holes in the valve housing for
the 2-56 mounting screws. |
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| Main Valve Sleeve: The sleeve is
turned from brass rod. The OD will be adjusted so that it is a
sliding fit in the valve housing. The sleeve will be secured
and sealed with Loctite 620.
All the grooves are initially cut 0.04" wide and used to align the
steam holes into the cylinder. The outside (steam input) grooves
will be widened toward the ends after the holes are drilled through the sleeve.
At least six 0.04" diameter holes will
be drilled in each
groove. The inside will be smoothed after the holes have been
drilled. The sleeve groove positions should be made as accurate as possible to
insure proper valve operation. |
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| Main Valve Piston: The main valve
piston is similar to reversing valve piston but longer with five
grooves for O-Rings. The piston will be turned from brass rod.
The O-Ring grooves should be turned as accurately as possible to insure proper valve
operation. It is convenient to tap each end 4-40 for a screw to
manually operate the valve during testing. |
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| Main Valve End Cover: The two end covers
are fabricated of brass or bronze . I'll probably turn the round
part from 1.375" diameter rod and then square off the edges on the
mill. Two end covers are required.
The end covers can be used as templates to drill and tap the
holes in the valve housing for the four #2-56 mounting screws. |
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| Upper Steam Head Large Alignment
Washer: This washer is cut from brass or bronze rod. The
washer is attached with a couple 4-40 FH screws. The screw
holes will be into the thicker part of the head where there is room
for 3/16" deep holes. |
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| Upper Steam Head Small Alignment
Washer This washer will probably be cut from brass or bronze rod
stock. This washer also retains the reversing rod seals. The washer will be fastened to the head with a couple
#4 FH screws into the thicker part of the head. . |
 |
| Reversing Valve Rod: The rod will
be made
from 1/8" stainless steel rod stock. A pair of 4-40 small
pattern nuts will be tapped 5-40 and screwed on the end of the
valve rod that fits in the piston rod. The nuts will be
positioned such that the valve rod has the correct amount of
movement (0.156") when the piston moves between the two extreme
positions. The nuts are tightened against each other to lock
them in position. The valve piston is screwed onto the
end threaded 4-40 and positioned properly and then held in place by
a 4-40 lock nut. |
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At this point the design is pretty well beat to death.
Guess it's time to make a few chips and see if it'll actually work.
