The Signal Foam Meter (manufactured by the Electro-Chemical Engineering Corporation of Chicago), was a device used to control foaming inside the boilers of steam locomotives. This equipment was used extensively on the Western portion of the CNR system, where water conditions contributed to foaming. If the water level inside the boiler becomes excessively high from foaming or from simply pumping in more water then is required, the locomotive may experience priming, which occurs when water enters the dry-pipe and makes its way to the cylinders, which can cause a considerable amount of damage to the machinery.
The device uses a series of electrodes of differing length, located in the boiler and housed in a trough. As the water level in the boiler rises due to foaming or from other causes, water enters this trough and makes contact with the electrodes which opens a valve that release the excess water. The excess water is expelled through a separator mounted in front of the cab, above either the engineer's or fireman's window. A control panel located inside the cab alerts the crew as to when it is in use, and also provides a means of testing the device. When the water level drops, and no longer makes contact with the electrode, the valve closes.
For additional information, look up Patent #1911756 at the United States Patent and Trademark Office.
Unfortunately, very few surviving CNR steam locomotives are equipped with a SFM (although several CPR engines equipped with the SFM are still in existence). Fortunately, CNR 5093 located at Casino Regina in Saskatchewan, is equipped with the SFM, and views of its major components can be seen below.
Wiring to electrodes is visible behind sand dome on engineer's side.
Close-up of wiring to electrode.
View of separator on fireman's side
Close-up of separator. Compare with the separator used with Continuous Blow-Down.
Close-up of control panel in cab.
Photos Courtesy Greg Dureau, Saskatchewan Gaming Commission.
Maintenance Regulation No. 14 (a-c)
Automatic Blow-Down Equipment
Electromatic Blow-Off Cocks
Roundhouse Maintenance
1. Testing Blow-Off Cocks:
Electromatic blow-off cocks must be tested at the end of each trip where the engine runs over more than one sub-division, or on arrival at home station where engine operates on one sub-division.
2. Conditions For Testing:
The boiler pressure must not be less than 100 lbs., the air pumped up to full main reservoir pressure, the dynamo running at 32 volts and test toggle switch placed in "OFF" position. Water level in glass to be at normal level.
3. Ball Valve & Seat:
See that shut-off valve is open. If steam and water appear at the drain pipe from automatic drip, it indicates that the ball valve in blow-off cock body is leaking.
4. Air Piston & Piston Rod Seat:
See that the valve in the air line to solenoid is open then place test toggle switch in cab in "ON" position. Red light should indicate and blow-off valve should open in about half a minute. If red light fails to indicate, examine 15 amp. fuse located above relay cabinet and if blown, replace. If fuse is okay and light does not indicate, renew bulb.
With blow-off cock working, no steam or water should appear at automatic drip, which indicates drip valve is seating properly.
At the same time observe drain pipe from vent hole in bottom of air piston cylinder. No steam or water should appear. If water and steam appear it indicated the piston rod is not seating properly on the seat in the bushing, or that the seats are cut.
5. Blow-Off Cock Fails To Open:
If blow-off cock fails to open after the red light goes on, test to see if air is blowing from the vent in bottom of solenoid valve, if not, the air supply is shut-off, the solenoid is stuck shut or gummed up, or the solenoid valve magnet coil is defective. If solenoid valve is working, test at vent pipe from bottom of air cylinder at blow-off cock, if a blow of air is detected it indicates piston cup is leaking and sufficient pressure cannot be built up to operate the piston. If piston cup is not leaking the piston is probably tight in cylinder and stuck.
6. Blow-Off Cock Fails To Close:
Place test toggle switch in "OFF" position, the red light should go out in about 15 seconds and blow-off cock should close.
If the blow-off cock fails to close after the red light goes off, the air piston is stuck in the cylinder, or the cab vent in the bottom of solenoid valve is gummer up, trapping the air in the air line to the blow-off cock.
7. Solenoid Valve:
If the solenoid valve is stuck or gummer up with oil, it must be cleaned out with kerosene. This can be done without removing solenoid by feeding kerosene into the inlet pipe. The outlet pipe should be disconnected to prevent kerosene getting down into air cylinder, and the outlet from the solenoid valve plugged. The dynamo should be running so that solenoid valve can be open by moving toggle switch to "ON" position to let kerosene through solenoid valve and the vent port.
8. Electrode:
If after following instructions in Paragraphs 6 and 7, the red light continues to burn and blow-off cock fails to close with water level normal, boiler should be cooled and electrode should be removed and examined for cracked insulator. If cracked, insulator should be replaced and defective sent to main shops for repairs.
If blow-off equipment fails to work when boiler is carrying high water and works okay with the test switch the boiler should be cooled and electrode removed to see if anode and cathode are tight on threads.
9. Permissible Repairs At Outstations:
The following repairs to electromatic blow-off cocks may be made at outstations:
Renewing ball valve and seat
Renewing packing cup
Renewing piston rod
Grinding and packing shut-off valve
Renewing air piston or ball valve springs
Grinding piston seat rod in bushing
Replacing defective magnet coil
Replacing defective electrodes
If other repairs are required, the blow-off cock must be removed and sent to the main shops for repairs.
If repairs are required to relay control panel this should be removed and sent to main shops for repairs.
10. Piston Cups:
When applying piston cups, the cup and piston rod must be assembled in jig to Drawing 1H-23219 so as to insure the O.D. of the piston being exactly concentric with the piston rod.
11. Caution Re Handling:
Blow-off cocks must not be struck with a hammer or other metal object if they fail to operate, as the walls are easily dented, and damage of this description may involve scrapping of the cock body.
Note: For complete operating and maintenance instructions see Electro-Chemical Engineering Corporation Handbook No. 1243.
Backshop Maintenance
12. Stripping And Cleaning:
When blow-off cocks are received for repairs, they must be dismantled, and the parts immersed in a lye vat or muriatic acid bath to remove scale and oil.
13. Air Cylinders:
The bore of the air cylinders must be checked, and if scored, dented, or tapered .003 of an inch, the air cylinder must be rebored. Only a minimum amount of metal must be removed to restore the bore to a smooth parallel surface. The limit for reboring will be .010" larger then the original diameter of 2.25".
14. Bushing Air Cylinders:
When the diameter of the air cylinder is greater then 2.26" the air cylinder must be bored out to 2-13/32" diameter and a bushing applied as shown on Drawing 1H-23316.
15. Pedestal Seat:
The bore of the pedestal seat must be checked to make sure that it is absolutely parallel to, and concentric with, the bore of the air cylinder.
If the bore of the pedestal seat is found to be cut, the pedestal seat must be removed and a new blank pedestal seat screwed in. The blank seat must be drilled, counterbored and faced with the tools shown on Drawing 2H-23220.
If the bore of the pedestal seat is found to be in line with the bore of the air cylinder, and the face of the piston rod seat on the pedestal is scored or pitted the seat must be refaced, using tools shown on Drawing 2H-23220.
16. Piston Rod:
If the seat on the piston rod is out it must be faced up and ground to a tight joint on the pedestal seat. When the piston rod is worn .010" smaller than its original diameter on the portion that goes through the pedestal seat, the piston, the piston rod must be scrapped. If the end of the piston rod that is exposed to the cutting action of the scale in blow-off water is cut or worn, the piston rod must be scrapped.
17. Packing Cup:
New packing cups must be applied to ll repaired blow-off cocks. Packing cups must be assembled on piston rod using jig to Drawing 1H-23219.
18. Ball Valve & Seat:
If the ball valve, or a ball valve seat is cut or pitted, or if the ball valve leaks under test, a new ball valve and seat must be applied, and the ball valve must not leak when blow-off cock is given final test.
19. Shut-Off Valve
The shut-off valve and seat must be ground in, faced or renewed as required. The threads on shut-off valve spindle and in shut-off valve body must be in condition. New packing must be applied to the stuffing gland.
20. Springs:
If the piston rod or ball valve springs are pitted, or have lost their tension, new springs must be applied.
21. Air Vent In Air Cylinder Cap:
When the cylinder cap is found to have an air vent drilled through the side of cap, this air vent hole must be peened over and plugged.
22. Testing:
To test the blow-off cock connect up an air supply to the air cylinder inlet and to the inlet or bolting flange of blow-off cock.
First, open the shut-off valve and turn on air supply to inlet of blow-off cock. If there is a leakage of air at the outlet of the blow-off cock the ball valve is leaking and must be repaired.
Next close the shut-off valve and turn on the air supply vent the packing cup is leaking, and must be repaired. If a leaking of air is detected at the outlet from the blow-off cock the shut-off is leaking and must be made tight.
Then plug the outlet of the blow-off cock and open the shut-off valve, leaving the air turned on to the air cylinder and inlet of blow-off cock. If a leakage of air is detected at the air cylinder vent the piston rod is leaking where it seats on the pedestal seat, and the piston rod and pedestal seats must be re-checked as described in Paragraphs 15 and 16.
It is important that the joint between the piston rod and pedestal seat be absolutely tight.
23. Air Solenoid Valve:
All air ports and passages must be cleaned out with kerosene to remove oil and gum. The valve plunger must be removed and cleaned and ground in on its seat.
After cleaning, the solenoid valve must be tested with air to make sure the valve plunger is not leaking at the seat.
The solenoid valve supporting stud is drilled to provide for venting of air from blow-off cock air line when solenoid valve closes.
Supporting stud serves as an exhaust air passage and must be renewed when orifice wear causes excessive loss of air pressure, thus making automatic blow-off valve inoperative. When support stud is replaced, check to see that valve seat has a 3/32" orifice. If not, replace with seat having required 3/32" orifice.
After the air solenoid valve has been cleaned, checked and tested, it should be sent to the Electrical Dept. for inspection of the coil and application to the locomotive.
