What Is a Slave Cylinder?

A slave cylinder on a white background.

A slave cylinder is an important part of the clutch system in your manual transmission vehicle. In fact, the slave cylinder is found in a lot of different industries where hydraulics and pneumatic systems are in place. Slave cylinders, while very important to a vehicle, are also found in industrial plants, airplanes, trains, medical instruments, and recreational vehicles. A slave cylinder does not actually have to work alone. There can be multiple cylinders in a series to help with a particular performance.

How They Work

A slave cylinder is an item that can be lengthened, or shortened, in response to some sort of actuation demand from another part. This lengthening or shortening then either pushes another cylinder, or balances the pressure of fluid from one position to another to have an effect on a moving part like a clutch, brakes, or large machinery parts like a backhoe bucket.

Working Together

Some applications where slave cylinders are used can find them working together in a chain. They are all commanded by one master cylinder which is at the beginning of the line. This helps larger machines operate more efficiently by taking away from of the complex mechanics. This works great when there is one part that moves, but needs to have another part move with it. As the master cylinder is actuated, it will then start another slave cylinder into action at the same time.

A Real World Example

To give a real-world example of what a slave cylinder's operation is like, you can use a bottle jack. This type of jack is actually made useful because of two different slave cylinders. The first is the master cylinder which is used by the jack handle to pump up the middle cylinder. This larger cylinder is the part that actually does the lifting. As the one moves, it actuates the other into action by a reaction to the force applied to it. Without this type of action, it would take a lot more force to lift a car.

Car Slave Cylinders

While the clutch slave cylinder that works the clutch when the clutch pedal is depressed is called a slave cylinder, there are plenty of different types of slave cylinders found on a car. They will go by different names, but they perform the same operation. They are found in the brakes as a brake cylinder, or wheel cylinder. They can also be found in the power steering system.

Pressure Necessary

While a slave cylinder is pretty much a lever that can force different types of work to be completed, it must be pressurized. This can be done through the use of either hydraulic pressure or pneumatic pressure. In a hydraulic system, like brakes on a car, you will find a master cylinder that has a reservoir of brake fluid. This fluid is then moved through the different slave cylinders in order to actuate the wheel cylinders. In a pneumatic system, like found in a truck's air brakes, the build-up of air pressure moves the different cylinders into action when the toggle for the air brakes is depressed.