About Tridak

Product Line

How To ...

Warranty Info

Contact Us

Dispense Valve Model 826

The model 826 (patents pending) is a dual piston, pneumatically operated, normally closed pinch valve with suck back. The 826 features precise, lockable controls to facilitate the adjustment of three critical parameters: 1) the flow rate through the valve (i.e., the amount the tube opens), 2) the amount of tube closure (which insures the accuracy and repeatability of operation and greatly extends tube life and 3) suck back (which allows 3 things: 1) clean shut-off of stringy materials, 2) prevents the formation of a droplet at the end of the nozzle, 3) minimizes the "skinning" over of materials that tend to dry out at the end of the nozzle).

Operation

Startup - When the customer supplied 3-way, spring returned, normally closed, valve (which can be operated electrically, pneumatically or manually) is off (un-actuated), the pinching surface of the upper, spring closed, piston prevents flow by collapsing the tube. The patented pinch stop adjustable screw limits the amount of pinch which limits the stress on the tube (this greatly extends tubing life and insures shot to shot repeatability). The blunt lower piston is held in its open position by a spring. The adjusting screw which determines the amount that this piston will close the tubing when its actuated is set to a position that will allow approximately a 50% tube closure.

Dispensing - When the customer supplied valve is activated the adjustable stop. This stop controls the amount the tube opens which, in turn, controls the rate of flow through the tube. These actions, combined with nozzle size (if a nozzle is used), fluid pressure, and the amount of time the 826 is open, governs the amount of fluid dispensed. Simultaneous with the action of the upper piston, the lower, blunt piston moves forward until it stops against the adjusting screw. This causes the piston to partially occlude the tubing.

Shutoff - When the customer supplied valve is deactivated (at the end of the dispense cycle) the actuating air exhausts. This allows the upper piston spring to move the piston forward where it once again pinches the tubing. At precisely the same moment the lower blunt piston is also released so that its spring can also return it to it original position. This action allows this portion of the tube to return to its normal (open) shape. It is this return to shape from its partially closed position (which is adjustable) that creates a precise suck back. The valve is now ready to repeat the cycle. Fine adjustments can be made to both flow rate and suck back to obtain the required results.

Pinch Tubing
Tridak supplies 3 ft. of 3/16 O.D., 1/8 I.D. Urethane Tubing and the appropriate nozzle adapter with the valve as standard. We stock a variety of other materials: Teflon®, Silicone, Vinyl etc., for special orders. Most materials have a life in the 2 to 20 million cycle range. Materials such as Natural Rubber or Silicone may have a life of billions of cycles. Please consult Tridak for availability of nonstandard items.