For years, diaphragm valves were the industry standard for fluid or media control in tubing fluid paths; they had no internal cavities that could trap product, allowing the valve to be completely drained and eliminate hold-up volume. While not completely cleanable, diaphragm valves were the best option available to be used over and over. However, pinch valves have now emerged as a superior product for single use or frequently changed process applications, offering a no-fail solution, along with easy maintenance.
Because of their safe and reliable processing, pinch valves can be used reliably in both upstream and downstream processing, as well as in formulation and filling. A pinch valve hinges over and clamps on the outside of the tubing, and its handle is tightened down to pinch off the line. Designed for one single use or single product run, the tubing is made to be thrown away after use, and any residue is disposed with it.
Pinch valves offer a constriction-free flow
The characteristics of fluid flow inside a valve are important for many products. When using a pinch valve, the tube is clamped from both sides to stop the flow, and when not in use, the interior of the silicone tube element is completely unobstructed; there are no internal components to restrict or retain any media. Therefore, fluids move through the tubes freely, and because the system is designed for single-runs, pinch valves are optimal for sterile and aseptic applications.
On the other hand, diaphragm valves do not allow constriction-free or direct fluid flow. Instead, they work by reducing the pipeline diameter in the area of flow and redirecting the product flow, which impedes quick, direct media transport through the pipeline. As a further complication, they are sometimes prone to developing encrustations due to their design. Because diaphragm valves usually close on one side, accumulations can form on the opposite side. This problem occurs because of the diaphragm valve’s contact pressure applied to the media. Over time, these encrustations can build up, causing other blockages and making transportation of the media more difficult.
Transport of difficult media
Because of the simplicity of their design, pinch valves easily handle viscous or difficult fluids. The interior of the silicone tube element is completely unobstructed, and its crevice-free design allows unhindered flow of fluids. Pinch valves have no bonnet/diaphragm interface, which eliminates a potential entrapment area.
Compare the pinch valve to a diaphragm valve. When fully open, pinch valves offer zero-restriction in the process line. Diaphragm valves, on the other hand, have a vena-contracta (internal restriction) that is inherent in their design where the body slopes toward the shutoff point. Even when fully open, this internal slope creates a restriction in the fluid path (lower Cv) which can cause turbulence and additional backpressure on the system. In a process line with a number of diaphragm valves this can result in the requirement for additional pumping energy which would not be required if pinch valves were to be utilized. Finally, by nature, a diaphragm valve has a flange on which the diaphragm and bonnet are mounted. The interface between this flange and the diaphragm has been the topic of much discussion over the years as it is difficult to guarantee that it is not a potential product entrapment area.
Reduces the need for cleaning
Pinch valves require no cleaning, as the silicone tubing is the only component that comes into contact with the media, and the tube is immediately disposed of after the run has been completed. This is not the case with diaphragm valves, which require extensive cleaning: a CIP (clean-in-place) system must be used to flush the valves with chemicals and then sterilize it with steam.
Eliminates replacement challenges and maintenance issues of the diaphragm valve
There are a minimal number of mechanical parts in a pinch valve, and they are designed such that no tools are needed for quick assembly or disassembly around the tubing. Operators are easily able to manage the tool free-clamp on in a quick three-step process and can change out the element in as little as 30 seconds, thereby saving valuable process time. The simplicity of pinch valve design also eliminates the need for more technical staff on hand to handle tube change-out; it also removes the need for regular maintenance.
The re-installation of diaphragm valves is more complex and involves disconnecting four bolts and then adjusting the valve to the correct torque specs. Tools are needed to conduct this task, meaning that operators are unable to complete the work. In these scenarios, a work order would need to be submitted to a maintenance crew to handle the task, resulting in inefficiency, delays, and additional manpower. Finally, due to the diaphragm valves’ complexity, there is the potential risk that they can be reassembled incorrectly.
In addition to the low maintenance requirements, unobstructed flow, and easy operator use, other benefits of the pinch valve include the following:
- No risk of failure
- No risk of cross-contamination
- Quick closing compared to diaphragm valve
- Wide range of sizes available
- Light-weight design
- Zero leakage
- Durable and resistant to wear
- Manual and automated versions available
- 100% tight seal after closing
- Compact construction; little space is needed beyond the pipe connection
Acuity offers pinch valves for new and upgraded systems
Offering products from Fluidline Technology, Acuity has access to top-of-the-line pinch valves in six standard sizes. Whether you are looking to upgrade your current diaphragm valve system to eliminate maintenance issues or start a new fluid system from scratch, the company’s expertise in pinch valves can help fit you with one that meets your needs.