Valves pinch

Pinch The industrial equivalent of controlling flow bv pinching a soda straw is the pinch valve, Mves of this tvpe use fabric-reinforced elastomer sleeves that completely isolate the process fluid from the metal parts in the valve. The valve is actuated bv applying air pressure directly to the outside of the sleeve, causing it to contract or pinch. Another method is to pinch the sleeve with a linear actuator with a specially attached foot. Pinch valves are used extensively for corrosive material service and erosive sliirrv senice. This type of valve is used in applications with pressure drops up to 10 bar (145 psi),... 

Pinch valves that have no packing to leak can leak if the tube breaks. 

Consequently, more elaborate designs had to be tested and/or developed for this application of pneumatic conveying. The following two valves have been found useful in particular areas. Note that in each case it is imperative to ensure fast actuation time (e.g., 1 second for a 100 mm nominal bore NB valve and a few seconds for a 300 mm NB valve, if possible). Large-bore solenoid valves and quick-exhaust valves usually are required for this purpose. Also, note that each one of the following valves provides a full cross-sectional area of flow in the open position and a 100% seal in the closed position. One of the major problems of air-on-sleeve pinch valves is that they do not provide these important features for pneumatic conveying applications (e.g., a small hole in a closed sleeve quickly erodes due to the subsequent high velocities of air and solids). 

Figure 18. High-pressure pinch valve (Larox Pty Ltd).

Timms, G., Pneumatic Conveying - a New Application for Larox Pinch Valves, Larox News, 14 8-11 (1992)... 

Pinch valves were introdueed in 1996 as an improvement in flow path compared to diaphragm valves. They have achieved some success, especially... 

A test system, controlled by personal computer (PC), was developed to evaluate the performance of the sensors. A schematic of this system is shown in Figure 3. The signals from the sensors were amplified by a multi-channel electrometer and acquired by a 16 bit analog to digital data acquisition board at a resolution of 0.0145 mV/bit. The test fixture provided the electrical and fluid interface to the sensor substrate. It contained channels which directed the sample, reference and calibrator solutions over the sensors. These channels combined down stream of the sensors to form the liquid junction as shown in Figure 1. Contact probes were used to make electrical connection to the substrate. Fluids were drawn through the test fixture by a peristaltic pump driven by a stepper motor and flow of the different fluids was controlled by the pinch valves. 

The plastic tube technique can also be used to mitigate the variable shift that occurs with liquid loss in the bubbler system when it is not refilled. In this case, simply move the pinch valve to the appropriate spot to rebalance the system. 

For testing at very low pressures the pinch valve and plastic tubing works, but at higher pressures tubing must be stiffer and reinforced and a pinch valve may not be able to maintain pressure without leaking. 

Fluid flow is controlled using solenoid isolation valves V ( 075T2NC12), diaphragm micropump P ( 120SPI12), and a 3-way pinch valve PV ( 075P3MP12). These devices were purchased from Bio-Chem (http //www.Bio-Chem.com). The system can either be run in a manual mode with full control or in batch mode for user-free operation. The latter is based on a 24 vial holder carousel, with rotational and up-down stepper motors. 

Fig. 19 Schematic of the CWBP. WF - waste port for the fluid, DF - fluid port for denature solution, S/B - port for sample and buffer, can be connected to a carousel dip probe, PV - 3-way pinch valve, V - isolation valves,...

The clamp valve consists of a flexible PTFE tube and a clamp. It is somewhat similar to a pinch valve, but, unlike a pinch valve, the tubing is not kinked, creased, or pinched. 

Completion of the Incubation time is detected by the LAS error-detector assembly, which monitors the analytical stream at the outlet of the Incubator. The microprocessor activates the magnets and, as stated above, the solid-phase antibody Is trapped while the free antigen washes through. The pinch valve is... 

Thermomechanical Valves, Fig. 16 SMA pinch valve, (a) Schematic of the valve (b) photograph of the valve... 

Pemble CM, Towe BC (1999) A miniature shape memory alloy pinch valve. Sens Actuators 77 145-148... 

Static pinch valve The feed tube from the product tank passes underneath the pneumatic pinch cylinder. When the valve is closed, the pneumatic cylinder closes the tube. When the cylinder opens, the product flows through the tube to the dispenser nozzle. 

A static pinch valve can be mounted on a bench station, or alternatively, on an automatic line. A typical bench application would be bonding the ends of a rubber extrusion to make up car door seals. In the case of an automatic line, a free-fall drop could be dispensed on to a component part located beneath the static pinch valve or, alternatively, a bead applied to a component part as it traverses beneath the pinch valve nozzle. 

Pressure time using advancing valve The advancing pinch valve is utilized in operator-paced or fully automatic lines where the component part itself cannot be moved to the valve nozzle. The advancing pinch valve, which can be between a stroke of 25 and 150 mm (1 and 6 in), advances the application nozzle to the component part. The dispenser valve then opens, allowing a metered quantity of product to flow through the valve nozzle on to the component part. The valve then closes and the advancing cylinder retracts from the nozzle. In this way dots or continuous beads of product may be applied. 

Pinch valves are essentially a short length of rubber or plastic hose which is supported in such a way that it can be flattened between two bars that are moved towards each other when the operating hand wheel is turned or compressed air applied. It is a very simple and trouble-free valve but it is limited to those chemicals that do not attack the tube material. 

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