Switch for water pump and valve. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Home, household, hobby
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In the private sector household, as well as in greenhouses, a water pump is often used in conjunction with a voltage controlled water valve for water supply, heating and irrigation. When turning the pump and valve on and off, the appropriate switching order must be strictly observed to prevent water hammer that occurs when the valve is suddenly actuated and the pump motor is rotating. When turned on, the valve is first turned on, and then, after 1 ... 2 s, voltage is applied to the pump. When turning off, on the contrary, the pump is first turned off, and then the valve is closed. This can be done with two switches, but during operation there is a chance of accidentally mixing up the switches, which can lead to a rupture of a thin section of the pipeline and even to a breakdown of the pump.
To avoid such troubles, you can assemble a simple switch on two relays that turn on and off in a strictly defined order when one switch is closed. A schematic diagram of such a switch is shown in the figure.
(click to enlarge)
When the switch SA1 is closed, the relay K2 is activated, and through the contacts K2.3 the unlocking voltage is supplied to the valve. At the same time, contacts K2.1 and K2.2 close, which respectively supply voltage to relay K1 and connect capacitor C3 to the power supply circuit of relay K2. However, the relay K1 will only work after a certain time, which depends on the capacitance C2 and the resistance of the resistor R2, which ensures the turn-on delay. With its contacts K1.2, relay K1 connects a water pump to the network. Contacts K1.1 disconnect the capacitor C2 from the relay K1 itself. The capacitor is discharged through resistor R3.
When turned off, i.e. opening the switch SA1, the relay K1 opens first, since the capacitor C2 is disconnected from the relay power supply circuit. Relay K2 will open when the capacitor C3 is discharged, which provides the turn-off delay time. Thus, the necessary order of switching on and off the water pump and valve is ensured.
The author used relays K1 and K2 of the TGL 200-3796 type in the circuit for a voltage of 24 V and with a winding resistance of about 1 kOhm. When using the values of the resistors indicated in the circuit, and the capacitor C2 with a capacity of 2200 μF and C3 - 470 μF, the delay time for turning on and off the relay corresponded to 1,5 ... 2 s. The supply voltage coming from capacitor C1 is about 32 V, while there is a voltage of 20 V on the relay windings, which ensures reliable operation of the relay.
In the circuit, you can use various relays for a voltage of 12 ... 48 V, selecting the appropriate capacitors C2 and C3, providing the necessary response and release delay, as well as the appropriate supply voltage.
When using the above relays for 24 V in the circuit, you can use a transformer with a voltage on the secondary winding of about 24 ... 26 V. Capacitors C2 and C3 must be at least 25 V. The type of capacitors used in the circuit can be any, for example K50-35. Diode bridge VD1 can be replaced by KTS402, KTS405 with any letter index. Diodes VD2, VD3 are replaceable by any other rectifier diodes, such as KD105, KD212.
Author: I.A. Korotkov
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