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Tech Pull Valves .:

Pull valves, like pinch trigger valves, are devices for controlling water flow through a water blaster with the use of a trigger mechanism. Akin to pinch trigger valves, pull valves can allow water (or air) to pass through the valve in either direction when open; 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. However, pull valves are technically more related to  spring-based check valves in how they operate, though there are definite distinctions because of the need to be manually operated. 

Parts of the Valve:

A pull valve is comprised of several (seven or more) parts:

  • trigger - where the user's finger contacts the system
  • wire/trigger rod - transferring the force of the pull from the trigger to the valve
  • lever - multiplies the force from the finger-pulled trigger towards pulling the valve open
  • pin - transfers the force from the moving lever towards moving the plug
  • spring(s) - the primary spring is used to push the plug and pin back to the closed position; there are also often one or two secondary springs that help to push the trigger as well as to control the force applied between the lever and the pin
  • plug/plunger - seals the opening when the valve is closed
  • housing - holds the other pieces in place and retains pressure until the plug/plunger is pulled from the opening

Water Blasters that Use This Valve:

Some blasters that use pull valves include:

Functional Steps:

Pull Valve

Closed:

When there is no significant pressure on the trigger (either from internal or external force), the spring pushes the trigger forward. This, in turn, pushes the plug securely against the forward opening of the valve, sealing it and preventing any water (or air) from escaping. Thanks to the geometry of the valve and the plug, increased pressure within the blaster will only serve to push the plug harder against the opening and will not result in the valve opening. As such, some sort of pressure relief valve at another point in the internal tubing assembly is highly recommended for, without one, it would become possible for too much pressure to be pushed into the water blaster, resulting in structural failure at some point of the assemble (typically at tubing connection joints)

Partially Open:

Applying pressure using one's finger on the trigger will pull on the lever, causing it to pivot about its point of attachment. The lever, in turn,  is set up to apply force on the pin to pull it outwards from the valve. Depending on the position of the lever's pivot point versus the location of where the pin makes contact, some force amplification will occur at the cost of reduced lateral motion.

As the lever pulls on the pin, this both pulls the plug from the pull valve's opening as well as compresses the internal spring. The distance the plug is pulled from the pull valve's opening controls the amount of permissible flow through the opening; the farther out the plug is pulled, the greater the potential flow through the valve becomes. Of course, the result flow rate also depends upon the amount of pressure initially exerted on the water as well as the diameter, length, and shape of the connective tubing leading to and coming out from the pull valve assembly.

Fully Open:

Depressing the trigger completely pulls the plug to be pulled to a maximum distance away from the pull valve's opening, allowing for the greatest amount of flow through the valve. The maximum distance the plug can be pulled out of the pull valve's opening depends on the internal space within the valve as well as the permitted range of motion given to the lever to apply onto the pin. As can be seen, the path water (or air) must pass through the valve is not linear.  Thus, for best flow results, the optimal fully-open position of the plug would be such that it is out of the direct flow route from the entry point to the exit point of the valve.

Flow Analysis:

As can be seen illustrated in the diagram above, there is no direct path for water (or air) to flow through the pull valve in the open state. Even when fully open, water (or air) may enter straight into the valve, it must be deflected twice to reach the exit opening. While pulling the plug out further permits more water (or air) to flow through the valve, once the plug is pulled far enough that it no longer obstructs the direct flow of water from the entry-to-exit points, pulling the plug further does nothing to improve flow rates.

Strengths and Limitations:

The pull valve is, more-or-less, a modified spring-based check valve that allows a user to manually open (activate) the valve when desired. Since the goal of the pull valve is to prevent flow until the user desires it, the valve is oriented in a opposite direction compared to how a spring-based check valve would be for forward flow.

Being spring-based, this valve rests in its fully-closed position, preventing undesired flow. As pressure within the internals of the water blaster increases, due to the orientation of the pull valve, this actually closes the valve tighter, making it harder to open. This is where the force amplification from the angle of the lever to the trigger rod versus pin connection comes into play. Optimal pull valves are designed such that even at maximum allowable internal pressure, the force of an average user's finger pull should be adequate to operate the valve without too much stress. Of course, those with weaker finger muscles may find operating some pull valves more difficult. There are also the cases in which the amount of internal pressure created is greater than intended (possibly due to a pressure relief valve not operating as well) which can also make a pressurized water blaster's pull valve much more difficult to use.

Interestingly, as noted above, since pull valves are more-or-less manually operated spring-based check valves, they can be used as such.  For the Super Soaker Super Charger (SC) series as well as Speed Loader Water Guns, their nozzle-based pull valves were used at times as spring-based check valves when they were filled via their nozzle from a hose-based water source. During nozzle-based filling, the force of the water from the hose would apply enough force to push the nozzle's pull valve open, allowing water to fill the blaster.

While not perfect for creating laminar flow, pull valves work much better than pinch trigger valves and allow for much greater flow rates. As such, these valves are still commonly found on many current water blasters.

 

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