Pinch trigger valves are the simplest way to control water flow with the use of a trigger mechanism. Unlike unidirectional check valves (e.g. ball bearing check valve, spring-based check valve, and rubber gasket valve), pinch trigger valves can allow water (or air) to pass through in either direction. The purpose of this valve is not to control flow direction; it is simply for controlling whether flow should occur or not, allowing the water (or air) to move in the direction from highest to lower pressure.
Parts of the Valve:
A pinch trigger valve is comprised of three main parts: the trigger piece, soft (malleable) tubing, and a spring (can be a coiled or linear spring set-up). The trigger, spring, and tubing must, of course, be fixed to the water blaster's housing in order to properly operate.
Water Blasters that Use This Valve:
Some blasters that use pinch trigger valves include:
When there is no significant pressure on the trigger (either from internal or external force), the spring pushes the trigger down/forward. This causes the trigger to squeeze (or pinch) the soft tubing, forming a seal to prevent flow through the tubing (hence, it's name "Pinch Trigger"). The tightness of the seal depends on the softness of the tubing, the strength of the spring used, and the shape of the part of the trigger that pinches the tubing.
Applying pressure using one's finger on the trigger will cause the inner assembly to pivot, thus allowing the soft tubing to open since the trigger and spring would no longer be pinching down on it. If the trigger is only pulled part way, the amount that the tubing can expand will be limited, thus not allow for full free flow. In that sense, the pinch trigger valve is an analog valve, allowing for differing degrees of openness depending upon how far the trigger is pulled.
As one may predict, if there is enough force within the tubing due to pressurizing the water on the inside, the water can also push on the trigger to open the valve slightly. In older pinch-trigger-based water blasters such as the original Super Soaker 50, there was no added pressure relief valve since the pinch trigger offered similar functionality without the need for an additional part.
Depressing the trigger completely allows the soft tubing to expand farther. However, even if the trigger is no longer in contact with the tubing, typically the tubing, itself, retains some deformation and never ends up perfectly open. As such, the pinch trigger device in some ways prevents a water blaster from operating at its maximum capability due to the undesired deformation of the tubing. That said, in most cases, the amount of power lost due to the imperfect flow through the pinch trigger valve is negligible since most pinch trigger tubing has low internal diameters, thus not able to permit much greater flow.
As can be seen illustrated in the diagram above, if the tubing were perfect, one could have perfectly linear flow through the valve when the trigger is completely depressed. Unfortunately, most of the types of soft tubing used end up deforming from being pinched and never completely open even when the pressure from the trigger is released.
Strengths and Limitations:
Pinch trigger valves are one of the simplest trigger control systems for pressurized water blasters available. Able to serve both as a trigger and allowing pressure relief when excess pressure is pushed into the internals, pinch trigger valves work well for smaller air pressure blasters that can afford to use smaller, ofter tubing between the pressure chamber and the nozzle.
Of course, the pinch trigger valve has several limitations. One issue is that if larger flow rates are desired when the valve is opened, this would require both that the tubing inner diameter is increased as well as the size of the trigger and spring needed to clamp down on the tubing to close it. However, as tubing diameters get larger, it also becomes more difficult to fully seal the tubing simply by pinching down on it. Thus, maximum flow rate is hampered by the availability of larger, yet soft tubing that will not get brittle or stressed after prolonged compression.
Another major issue is that since the tubing is pinched closed by the trigger, if the wrong material is used for the tubing, the tube may stick and no longer open even when pressurized and the trigger is depressed. Some tubing material gets sticky and will strongly seal if left clamped together for too long. This was an issue in many of the early Super Soaker 50s when they were first made.
Moreover, even when non-sticking tubing is used, the fact that the tubing ends up compressed for long periods of time, tubing gets distorted and fails to open fully when the trigger is depressed. As such, the already lower diameter tubing ends up with further restricted flow past the trigger, thus reducing the available water pressure at the nozzle. Rotating the tubing (if possible) can help alleviate the extent to tubing deformation, but this is not always possible to do.
While not directly related to this valve technology, pinch trigger valve water blasters also tended to use fairly long lengths of tubing between the pressurized chamber and the nozzle. Longer tubing also reducing available force at the nozzle due to drag as the water flows through the tubing (more on this coming soon).
While pinch trigger valves worked well for the first generation of pressurized water blasters, later trigger-controlled valves perform their function more reliably and permit larger flow rates for the nozzle.