A common method to energize solenoids in multi-cylinder systems, when possible, is to drive them through which device?

• A. Direct connection
• B. Power supply through transformer
• C. Pushbutton control
• D. Control relays

Answer: (D)

Control relays are used to energize solenoids in multi-cylinder setups because they provide safe, scalable control by letting a low-current control signal switch the higher-current solenoid coils. This isolation protects the control devices from the inductive load and allows a single control action or a logic sequence to energize multiple solenoids through the relay contacts. It also supports sequencing and interlocks, and makes wiring simpler and more reliable. A transformer may be used to supply the correct voltage to the relay coils or to the control circuit, but the actual energizing of the solenoids happens through the relay contacts. Directly wiring solenoids to control switches would overload them, and relying on pushbuttons alone isn’t practical for coordinating multiple coils. Hence, driving solenoids through control relays is the common method.