Toilets
I thought it would be fun to talk about toilets since we interact with them daily, yet, mostly ignore them and their operation.
Components:
- water inlet
- diaphragm valve
- Tank open to atmosphere (usually covered)
- Level Indicator with mechanical linkage to diaphragm valve(2)
- Chain operated stop-check valve
- Bowl also open to atmosphere
- S-bend outlet pipe to sewer/septic system
Operation
During normal operation, the water level in the tank is controlled by feedback from the level indicator to the inlet valve. When the level is low, the valve is open filling the tank. When the level is high, the valve is closed. The water level in the bowl is determined by hydrostatic pressure in the s-bend of the outlet pipe. The toilet is flushed by manipulating the check valve releasing water from the tank to the bowl. When the bowl water level exceeds the height of the s-bend, a syphon effect empties both the bowl and the tank. once the check valve is closed, the tank refills to the appropriate level, so the process can be repeated as needed.
FMEA
It may seem contrived to talk about Failure modes and effects of a toilet, but actually a running or overflowing toilet can cause a lot of damage not to mention inconvenience.
Failure Mode | Effects | Cause(s) | Occ | Det | Sev | RPN |
---|---|---|---|---|---|---|
Low inlet pressure | long tank refill time | utility issue | 1 | 8 | 3 | 24 |
high inlet pressure | Short tank refill time, tank overflow, noisy | utility issue | 1 | 8 | 8 | 64 |
valve stuck open/leaking | tank overflow, wasted water, noisy | level indicator failure, corroded valve | 3 | 7 | 8 | 168 |
valve stuck closed | unable to flush bowl | level indicator failure, corroded valve | 3 | 7 | 5 | 105 |
low tank level | unable to flush bowl | inlet valve closed, check valve open | 2 | 5 | 5 | 50 |
high tank level | tank overflow | inlet valve open, check valve closed | 2 | 5 | 8 | 80 |
check valve stuck closed | unable to flush bowl | broken chain, corroded valve | 3 | 2 | 5 | 30 |
check valve stuck open/leaking | bowl overflow, unable to refill tank, unable to flush bowl | corroded or physically blocked check valve | 5 | 5 | 5 | 125 |
bowl level low | unable to flush bowl | outlet leak | 2 | 1 | 5 | 10 |
bowl level high | bowl overflow | clogged outlet, check valve open | 9 | 2 | 8 | 144 |