Hydraulics 101: Part 6, Solenoids
By Kevin Whipps
You have batteries to provide power, and you have pumps that need power — so you need a way to get power from one to the other. You can’t just wire it straight through, though, because then the pump would constantly be on. So how do you do it? You use solenoids, which we’ll discuss today.
A solenoid is a switch, plain and simple. You have power coming into it, and a wire that activates it at the other end. Once activated, the solenoid allows power to flow from the batteries to the pump.
Solenoids are probably the weakest link in the hydraulic chain, but they’ve gotten better. Like a pump, a solenoid runs on 12 volts. With more voltage going to it, a solenoid can burn out. As a result, it’s very common to see rows of solenoids in series to compensate.
Prestolite recently came out with a solenoid block that I now use in every install. Essentially, they’re just three 24V solenoids in one case, but they work well. You can run up to six batteries off of one block, and they don’t wear out anywhere near as fast as your standard solenoid.
The problem happens when a solenoid sticks. It can either stick open or closed, but either way isn’t good. When it sticks open, so that the pump keeps running, it’s called a runaway.
So you’re wondering what to do with a runaway? Pull the ground. That’s why you always have a ground strap ready to go at any time. If a pump keeps running, since it’s pushing 5,000+ PSI, it can burst hoses, break pumpheads, and wreak all sorts of havoc. Have a quick release for your ground, and you’re good.
Note: a solenoid needs to be properly grounded to work well. To ensure worry-free operation, make sure the solenoid’s solidly bolted to the floor and that all mounting surfaces are ground to bare steel.
In part 7 of our continuing series, we’ll discuss lines and hoses.
