Cross Compound Compressor Design I  Cross Compound Compressor Design II  Cross Compound Compressor Design III  Cross Compound Compressor Design IV  Cross Compound Compressor Design V  Plumbing Parts List

The majority of the construction was described in Parts I &II.  In this part we fabricate the upper steam head and the steam valves.  We do the final assembly and also go though a test procedure to verify the correct operation of everything.

Upper Steam Head: Recall that I redesigned the upper steam head (HM562) after I was dissatisfied with one made from 1/8" brass bar stock like the other three heads.  The photo shows the head after it had been milled and the attachment holes drilled but before the outer surface had been sawed to the final contour.   I didn't have a 3/32 drill long enough to drill the full length of the exhaust passage.  The steam passage was drilled through to the exhaust passage and then the excess length of steam passage just to the right of the reversing valve  was plugged and silver soldered.   The hose connection shown in the photo supplied compressed air to test the plug.   This was also used later to test the valves.
Valve Housing: The passages were drilled in the HM563 housing before it was soldered to the head.  The photo shows the the housing upside down.  The two holes in the corners are for the screws that hold the housing to the head.    The screws sticking out of the housing identify the steam supply passages.
The housing is right side up in this photo.  The inter cylinder passages have been added and are identified by the screws and the two green plugs.
The housing and valve reinforcement (HM564) were soldered to the head and then the passages were drilled between the head and the housing. The next step was to mill the head to smooth the screw heads and any excess solder around the screw heads.
The slots between the vertical passages and the tops of the two cylinders were milled next.    Note that the holes between the head and the side steam ports have not been drilled yet.  Those passages were drilled after the valve was tested.  Air for testing was supplied via the hose shown in the first photo.
Main Valve Sleeve: The photo shows the main valve sleeve (HM567) after the grooves had been turned in the outside.  The next step was to drill the steam holes between using the grooves as guides.
After the steam holes were drilled the inside was finished with 400 Emory cloth.  The outside of the sleeve has a several thousands clearance with the housing.  The outside of the sleeve was roughed with coarse sand paper and then coated with Loctite 620 as shown in the photo.
A thin coat of Loctite was also applied to the hole in the housing and then the housing was slid onto the sleeve rotating it as it was slid into position.  The Loctite sets quickly where the pieces are close together (no air).  It stays fluid  where it is thicker and air is present.  As soon as the joint was firm --- after a couple minutes--- the lathe was turned on to spin the head and force any of the fluid Loctite in the groove to the outside away from the steam holes.     After the joint was solid (an hour or so) the sleeve was cut off from the stock.  Note that the stock in this photo is different from in the previous photo.  The first attempt  at installing the sleeve is shown here.  I was unhappy with the results so I heated the joint to about 700 degrees and then easily drove the sleeve out.  The next attempt was successful.
Main Valve Piston: This is the main valve piston (HM568) with the O-Rings installed.
Reversing Valve Piston & Rod:   The left end of the valve rod (HM572) is threaded 5-40 while the right end is threaded 4-40.  The upper part of the reversing valve piston (HM565) is threaded 4-40 and screws on the right end of the rod.   The two nuts on the 5-40 threaded part of the rod are 4-40 small pattern nuts that have been expanded to 5-40 with a tap..
Reversing Valve & Main Valve Caps: The reversing valve cap (HM568) is on the left side of the photo  with the Main Valve Caps (HM69) in the center and on the right.  The gouges in the main valve caps happened when the valve assembly slipped in the milling vise.   The gouges were filled with  JD Stick Weld before painting.

Assembling & Testing the Steam Valves: At this point the entire compressor can be assembled and tested.  I did that and it sort of ran, but not correctly.  After taking it apart dozens of times I decided it would be best to test it as it was assembled. 

Before assembling the valves, drill bits should be run into the valve passages that connect to the main valve sleeve to clean out any Loctite that may have flowed into the passages when the valve sleeve was installed.   Next, the set screw plugs are installed in the open end of all passages using a small amount of Loctite 620 as a sealer.    The two vertical passages from the main valve to the high pressure steam cylinder should  also be plugged with set screws but no sealer --- these plugs are used only for testing the valves.   

The valve cylinders and pistons should be lubricated with oil before inserting the pistons into the cylinders. Gaskets are required for the main valve end caps.   I cut all the gaskets from bulk  Compressed Aramid/Buna-N Sheet Gasket 1/64" Thick, (McMaster-Carr #9402K21).  The gasket and cap are not required for the reversing valve at this point.  The  reversing valve stem was attached to the reversing valve so that the valve could be operated manually.

The first test is to position the reversing valve in one of the extreme positions, apply about 30 psi to the steam input and dip the head in a bucket of water to test for major leaks.  Minor leaks around the unsealed set screw plugs on the main vertical passages are to be expected.  All other major leaks must be fixed so that sufficient pressure can build to operate the main valve. 

Once the leaks are fixed, the reversing valve can be moved between the two extreme positions and the operation of the main valve detected by the thump as it slams against the end covers.   If the thumps aren't detected, the pressure can be increased up to about 100 psi if necessary to get the piston moving.  After a few dozen operations my valve moved at about 30 psi input pressure.

After the main valve is found to operate properly, the head should be put in the bucket of water again and verified to have no leaks (except for seepage around the unsealed set screws) in either valve position.   All leaks including leaks out the exhaust passage should be fixed before proceeding further.

Assembling the Steam Engine: The next step is to assemble the steam engine consisting of the upper head the steam cylinders, the center piece and the pistons with rods.   At this point I choose to use the openings at the ends of the upper head for steam (compressed air)  input and deferred drilling the passages in the bottom of the head and the mating passages in  the channels down the sides of the cylinders.  The photo show the two 3/32" OD-1/16" ID tubes inserted in the passages that go to the bottom of the steam cylinders.   A very small amount of high temperature silicon sealer is spread around the tubes as well as around the slots  to the top end of the cylinders to improve the gasket seal.   Similar tubes (1/8" OD - 3/32" ID) as well as a little sealer are also used on the passages to the side ports.

Testing Steam Engine:  Air can be applied to the steam input and the engine should run.  My engine ran at about 50 psi initially.  Later after things loosened up and plenty of oil was included in the input it ran on ~20 psi input pressure. The animated gif at right shows the operation at about 30 psi input pressure.  The unit was positioned upside down so that the motion of the the end of the reversing valve  can be seen in the lower left corner (the reversing valve cap has been removed).  Note that this photo was taken during the reassembly after painting.  The little face in the lower left corner was placed there by the free trial software used to process the graphic file. The face is not placed there by software that has been purchased.

Before moving on to the steam engine  the pump should be submerged in water and checked for leaks around the head gaskets.  I had a few leaks that were fixed by tightening the head screws slightly.

Assembling the Compressor:   The air cylinder and lower head should be attached next.  The output check valves and all check valve plugs should be left off at this point.  Once all the head screws are in place, air can be applied to the steam input and the movement of the pistons verified.  The photo shows the pump after painting and reassembly.

.Testing input check valves and low pressure cylinder:  The input check valves and low pressure cylinder can be tested by covering the output of the inter cylinder check valves with a finger, one at at time.  The steam engine should stall if either of those outputs are covered.   If the engine doesn't stall, there is a leak someplace ---- use a water bucket or soapy water to find it.       

Test Tank:  I made a test air tank to help with the compressor testing.  The main part of the tank is some scrap gas pipe.  One end has reducing fittings and then a 1/4" ID hose that connects to the compressor output pipe with a hose clamp.   The other end has the gauge, valve and air quick connect shown on right.

Testing inter-cylinder check valve and high pressure cylinder:   The check valve plugs should be installed on the inter cylinder and output check valve housings at this point (the output check valves shouldn't be installed yet).   I then connected the test tank to the compressor and charged the test tank from the shop compressor (using the quick connect shown in drawing above) to about 75 psi.  If there are no leaks, the pressure should hold.  If the pressure bleeds down which mine did, there is a leak.  I put the compressor in a bucket of water, noted the leaks and fixed them (tighten head screws and check valve plugs).   Once that is stabilized, I used a  pin to push open each input check valve and verified that the pressure still held (this tests the inter cylinder check valves.)   Once this test passed, the output check valves were installed, but not the plugs.

Testing the output check valves: The output check valves are tested by charging the test tank connected to the output and the gauge observed to verify that the pressure holds.   If there is a leak, the bucket of water can be used to find it.  

Testing compressor sides:  The compressor can be tested next, one side at a time.  The output check valve plug is installed in one side and the compressor run with ~100 psi supplied to the steam input.   The test tank should charge to 30 psi fairly quickly and then the compressor will slow down.  The output check valve plug can be moved tot he other side and that side tested in the same way  (On my compressor, one side became really slow at lower pressure than the other side.  If both sides run, then  we can proceed to the next step.    

Testing the entire compressor:  The final test is to install all the check valve plugs and turn on the input air.  On my unit, the speed didn't slow down much until the pressure reached about 60 psi.  It then slowed gradually and became very slow at about 90 psi.  It continued to pulse until the pressure built to about 105 psi.    The graph below shows the pressure build up in the 50 cubic inch test tank.

Operational Glitch: I found one operational glitch ---- if there is a small leak the high pressure air piston will drift to one side and bottom on every stroke at high output pressure..  This causes uneven strokes and reduces the output rates.  I used a soap solution after the tank pressure got above 90 psi and quickly found several extremely small leaks around head gaskets (mostly on the steam side) and around the check valve plugs.  These leaks were fixed with a little snuggling of the head bolts and check valve plugs. (Car must be taken to avoid overt tightening the plugs to avoid squeezing out the O-Ring seal.)  

Steam condensing in the steam cylinders appeared to a major problem with the prototype.   Cocks were provided on both steam cylinders to drain the condensate when the pump was started cold.    The condensate caused no problem other than very wet exhaust on the single cylinder pump  I made for the shay.  I didn't expect to have a problem with this pump either.  As a test I submerged the pump in a bucket of water with the steam input open and managed to get quite a bit of water in the steam valves and small cylinder.  The pump started with no problem and passed the water through and out the exhaust.   I didn't allow a large amount of water to get into the compressor side since the contents of the input (larger - low pressure) cylinder must be compressed to fit into the output (smaller - high pressure) cylinder.  Since the water is essentially non compressible, the compressor will stall.  Loosening the inter cylinder or output check valve plugs will allow water in the compressor to escape. 

This wraps up the compressor for now.  I'll' come back and update these notes after I get the compressor running on a locomotives --- probably a year from now.   Arrangements for oil feeds to both the steam and compressor sides with be made at that time.

 

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