Most, if not all, manual dispensing guns utilize a smooth or ratchet drive rod. They utilize what is commonly referred to as a caulk gun mechanism where the drive rod moves forward as the trigger handle is squeezed. As the handle is released, returning to the initial squeeze position, the drive rod stops moving forward. This leads to a pulsating pressure on the cartridge plunger and on the materials(s) contained in the cartridge(s).
Another feature of the caulk gun mechanism is that more potential energy is developed with each squeeze than can immediately be utilized in the dispensing process. Thus the applicator keeps the handle squeezed until energy is converted to kinetic energy and used in dispensing. This initial excess energy must be stored somewhere, and the applicator is constantly squeezing the handle, which can be tiring.
With conventional manual guns, the excess energy generated is stored in two ways:
- Causing the expansion of the cartridges since the material(s) being dispensed cannot be compressed.
- The rod(s) of the manual gun bend and twist to absorb the excess energy. To utilize this energy, the applicator keeps squeezing the handle (or keeping it squeezed) until this energy is utilized in dispensing. If he wishes to stop the flow, he can release this force and lose it, typically by pressing a thumb-release mechanism. If the cartridge expanded and/or if the material had entrapped air, material may continue to flow even after pressure release.
The rods bending and twisting can lead to uneven pressure on the cartridge(s) plunger(s) leading to leakage out the back of the cartridge(s).
Emecole Metro Jake Dispensing Guns features a spring linked to the drive rod and designed to store the excess potential energy generated during the squeezing of the trigger handle. The spring becomes the point of least resistance, not the cartridge(s) or the drive rod. Thus the rods do not bend to cause leakage and the cartridge(s) do not expand. The excess energy is effectively stored by the spring. The spring in turn can release this energy by moving the drive rod forward even if the trigger handle is not being squeezed. Thus a continuous force is assured and results in a continuous flow of product, not an uncontrolled pulsating force. The applicator can release his grip on the trigger handle so that the applicator can control the force by which the dispensing is occurring. For example, in low pressure epoxy crack injection, it is best to maintain a pressure of 20-40 psi to assure that the crack fills totally and that the material doesn’t just flow thru the point(s) of least resistance (namely the larger sections of the crack). The spring to be recommended would be one that can store 40 psi when fully compressed (if a compression spring) or fully extended (if an extension spring); and can release down to 20 psi when it needs to be reactivated (by squeezing the trigger handle).
A high performance trigger handle mechanism can generate up to 100 psi with normal squeezing. This is more than is needed in many low pressure applications and the spring can control this. At the same time, some applications need most or all of the 100-psi power of the trigger handle (i.e. when dispensing paste material through a static mixer or caulk which is cold). A higher capacity spring is used for these applications.
The spring can also be utilized to effectively meter the amount of material to be dispensed. By attaching a hose with a pinch clamp at the tip of the cartridge nozzle or static mixer, the flow of material can be temporarily stopped. The applicator can determine how much material is dispensed over a given travel of spring. The trigger handle is then utilized to cause the spring to activate to that distance. With the release of the pinch clamp, the desired metered quantity of material will then be pushed out by the spring acting on the drive rod. This technique is especially useful in anchoring applications.
The latter concept is also very important in over-coming a problem associated with dual cartridge dispensing (as well as with any multi-component metering/dispensing). Dual cartridge dispensing relies on both components flowing uniformly through a static mixer to have the best mixing at the proper rationing. This is attained in time but initially the two materials may not flow at the same rate (because of differing viscosities and/or different surface tension values). Thus, when pressure is introduced to the cartridges, the materials are often not on ratio and therefore this part of the mix may not cure as desired. Dual cartridge dispensing typically involves small shot sizes which in turn requires often releasing of the pressure to stop flow of material. As you start up each time, the application may or may not be properly metered at the starting point (which could be a substantial part of the shot size when shot size is small).
A manual dispensing gun with a spring can effectively overcome this situation. By utilizing a hose assembly with a pinch clamp, it is practical to maintain pressure on the system and stopping flow with the pinch clamp. The spring maintains pressure on the system as flow is stopped by the pinch clamp hose assembly and the material flow can be started again without starting from zero pressure. The equilibrium is maintained and the materials flow at the proper and the desired ratio is maintained throughout the emptying of the cartridges. Use of hose assemblies for cartridge dispensing With a spring-assisted manual injection tool, the use of hose assemblies for cartridge dispensing offers several advantages.
- Allows dispensing and discharge control remote from the gun/cartridge system; control flow at hose with pinch clamp.
- Maintain pressure and mixed system equilibrium during dual cartridge processing (control flow with pinch clamping of hose, not by relieving tool pressure). Limit any lead/lag to beginning of operation not every time applicator starts and stops.
- To reach difficult areas, such as injection ports behind an obstruction (i.e. a hot water heater in a basement crack repair) or beyond the applicator’s reach.
- Control amount of discharge (meter the shot-size); especially useful in anchoring applications.