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 TM 55-1905-220-14-8
4-16. WATER CLOSET - MAINTENANCE INSTRUCTIONS (Continued).
(1) To initiate the water closet flush cycle, the activation valve (43) pushbutton is depresssed
momentarily. Pressing down on the activation valves flush button closes the normally opened (N.O.) valve
and opens the normally closed (N.C.) valve, directing vacuum pressure to the gravity timer (27). Metered
vacuum pressure is directed to the top of the gravity timer and through its normally opened (N.O.) 3-way valve,
back to the activation valve (43) hold down.
(2) Vacuum pressure on top side of gravity tinier (27) raises cams closing its normally opened (N.O.)
valve, cutting off vacuum pressure to activation valve (43) hold down. Activation 3-way valves return to their
N.O. and N.C. positions, directing vacuum to the gravity timer N.C. 3-way valves.
(3) Vacuum is cut off to top side of gravity timer diaphragm allowing weighted and spring-loaded cams
to fall, opening the 3-way valves to port vacuum to the water dispensing valve (38) and the 3-way vacuum
dispensing valve (34). Opening of the water dispensing valve (38) allows a pre-determined amount of water (2
pints) (.946 liters), to enter the water closet bowl. Opening of the vacuum dispensing valve (34) directs the
vacuum to, and opens the sewage discharge valve (49) to flush the water closet.
(4) The vacu-mechanical water closet is designed to have approximately a four-second flush cycle,
excluding a few second time lapse for cocking the gravity timer (27). The water closet is also designed for
limited water consumption per flush (2 pints) (.946 liters). Sequence and duration of the water dispensing valve
(38) and vacuum dispensing valve (34) is controlled by two cams of the gravity timer. The longer cam of the
two opens the N.C. 3-way valve which opens the water dispensing valve for a duration of approximately four
seconds of water flow. Water flow preceeds opening of the sewage discharge valve by a second. The short
cam opens the N.C. 3-way valve to the vacuum dispensing valve, which in turn opens the sewage discharge
valve. Discharge valve opens for a second for a vacuum and water flush. Discharge valve then closes and
water continues to flow for approximately two seconds to leave a small amount of residual water in the bowl.
Time periods for water dispensing and sewage discharge opening are designed to complement one another and
cannot be adjusted separately. However, the overall time span may be lengthened or shortened which will vary
the discharge opening and the amount of water dispensed. This can be accomplished by adding a longer
metering tube to the top of the gravity timer to lengthen the time span, or shorten the metering tube for a
shorter time span.
(5) There are two check valves in the vacu-mechanical water closet circuitry. The first is located at the
main vacuum supply and mounted stationary to the sewage discharge valve (49). The function of this check
valve is two-fold; first it maintains the control vacuum in the pilot circuit while the sewage discharge valve is
open and secondly, it prevents sewage and water from being drawn into the pilot circuitry. The second check
valve is located in the supply line
4-613
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