| 摘要 |
To protect the pump of a whirlpool bath against running dry and against blockage at the inlet, a pressure (or flow) sensor 14 senses pump pressure and generates a signal to keep a switch S2 in the pump motor electrical supply circuit closed. If the pressure signal ceases owing to blockage or running dry, the switch S2 opens. A manual override button 15 is held ON to close switches S1a and S1b in the power circuit for start-up. The sensor 14 and manual button 15 are preferably air pressure devices. Switch S1a is preferably an air-signal-operated latching switch whereby with the pump operating, the button 15 can be operated to switch the pump off. Relays RLA 1 and 2 may be used in conjunction with the electrical switches. A bleed hole may be provided between the button 15 and switch S1b to limit the period of time for which the motor could be run, with the bath empty, by prolonged inadvertent actuation of the button 15.
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