A pinch valve sometimes called a closed-end or open-end vent is a device that allows gas flow from a higher pressure to lower pressure. When the vent is closed, the flow of gasoline from the higher pressure side is constrained to the lower pressure side of that valve, which causes gasoline to be siphoned from the engine through the vent. The purpose is to avoid back feeding, which is what happens in open vent engines that do not have a safety valve between the two pressure sides. A closed vent engine will generate less horsepower than an engine with a vent that opens.
Closed vent engines use a rubber tube to achieve this. The rubber tube contains a mass of air that is forced between two sets of piston rods. As the engine is running, the compressed air spins the piston rods, which causes hydraulic pressure that forces a varying amount of fluid through the rubber tube. As the engine slows, so does the amount of fluid flowing through the tube, until it is no longer able to force fluid through the rubber tube when the engine is shut off.
The benefits of a pinch valve are many and can help an engine with poor airflow by achieving a closed seal between the top of the crankcase and the engine. The engine can then maintain a constant full bore speed. This is called pinching.
The benefit of a full bore speed is that more fuel can be burned per cylinder. It is also important for engines to have a full bore because without it the engine can only run at half bore speed, which limits how far an engine can go before it needs to idle again, and the level of fuel used per cycle.
The benefits of pinch valves are also good for controlling engine radiator heat and reducing sludge and moisture deposits from the intake charge. The benefits of full bore speeds are that the engine runs more consistently, which minimizes fuel consumption and emissions.
The main benefits of pinch valves are that they provide a reliable source of air control, and because they allow a consistent and controlled amount of fuel to be burned per cycle, they also help to maximize the life of the engine. Pinch valves also improve the performance of induction kits by allowing a stable supply of fuel into the engine.
Although the benefits of a pinch valve are many, several drawbacks need to be considered. One of these is that the actuator needs to be attached to a large pipe. This may limit the area in which you can use them, especially if there is not enough room for the actuator to be attached.
Another drawback is that the smallest and least expensive models are usually the ones that do not provide any benefits. These types of valves tend to be made out of steel, which can increase the weight and expense of shipping.
There are other methods to open a handwheel other than using a pinch valve. One method is called a kickback and is achieved by kicking the stem back so that the hand heel pushes the piston back.
Kickbacks tend to work better with larger engines, but can be used on small engines as well. You can also have your engine oil changed, which would cause your motor to kick back, but since most kickbacks are temporary, it will not affect your ability to drive your car.