A Sleeve Valve is a type of valve for piston engines that has a number of advantages over the more common poppet valve. as the name implies, this valve is constructed as one or more sleeves that typically fit around the piston inside the cylinder wall. Several ports (holes) in the side of the cylinder replace the more normal intake and exhaust ports on the head. Similar holes in the sleeve(s) open and close the ports like a poppet valve would, but do so by being rotated into position.

By moving the sleeve in one direction, the air is free to pass through the sleeve valve to the system. By moving it in the opposite direction, the supply is shut off and the air downstream escapes to atmosphere. It is compact, neat and aesthetically pleasing.

Another advantage of a system with sleeve valves is that the actual size of the ports can be easily controlled. This is important when the engine runs over a wide range of RPM, because the speed at which the air can move into and out of the cylinder is defined by the size of the duct leading to the cylinder and varies with cube of the RPM. In other words, at high RPM the engine typically wants larger ports that remain open longer in terms of one cycle, something that is fairly easy to arrange with a sleeve at the cost of a more complex gearing system.

Today sleeve valves are manufactured with newer materials and more notably, newer and dramatically better construction techniques that make a sleeve valve engine "tight" enough to prevent any oil leakage.

Sleeve valves fittings that provide an efficient in-line three-way valve are also offered. When the sleeve is moved to the "ON" position, fluid is allowed to pass through the valve. When the sleeve is moved to the "OFF" position, the outlet is exhausted to the atmosphere and fluid is prevented from exiting the inlet port. The valve can be attached directly on a device to be isolated and does not require mounting.