A Primer on Hygienic Diaphragm Valves
Processors needing to direct fluid quickly throughout their facility frequently utilize diaphragm valves. That's because they are:
- Versatile: suitable for use with a wide variety of fluids
- Sanitary: easy to clean and maintain
- Simple: contain few moving parts
- Secure: feature an anti-leak seal with a tight shutoff
The only difficulty for processors is deciding which diaphragm valve style to select. This article will look in detail at these specialized valves, which are primarily used in the biotechnology and pharmaceutical manufacturing industries for fluid flow on/off applications.
We will discuss:
- The function of diaphragm valves
- The purpose of diaphragm valves
- The materials used to make diaphragm valves
- The advantages/disadvantages of diaphragm valves in particular applications
What is a Diaphragm Valve?
Diaphragm valves have been around for a long time. In ancient Greece and Rome, individuals used this type of valve to control the water temperature and flow in hot baths. The diaphragm valve was modernized in the early 1900s by a South African mining engineer, P.K. Saunders, whose company continues to manufacture these types of valves today.
Diaphragm valves are perhaps one of the most configurable types on the market, well-suited for the highly sanitary processing needs of the biotechnology and pharmaceutical manufacturing industries.
Their versatility is due to the nature of how these valves work and their construction.
As the illustration below shows, diaphragm valves consist of a valve body and a flexible elastomeric membrane that combine to control the flow of a fluid. To close the valve, the membrane/diaphragm seals against a seat or weir.
Weir type diaphragm valves are the most common type of diaphragm valve. They are suitable for a variety of applications (e.g., pharmaceutical, food, and beverage applications) due to their high cleanability. They are also used in throttling applications.
The flexible diaphragm is connected to a support mechanism known as a compressor which is used to open and close the diaphragm.
- When the valve is open, the diaphragm is lifted out of the fluid flow path, and the fluid has a smooth, streamlined flow passage.
- When the valve is closed, the diaphragm is tightly sealed against either the seat or the weir.
The most common diaphragm valve configuration is two-port (also called a two-way diaphragm valve). Three-port or three-way configurations are also common. Much more complex configurations have multiple ports and may have more than one weir as well as more than one diaphragm and actuator. These complex configurations are used for mixing, dividing, controlling, draining, sampling, or feeding.
A significant advantage of this type of valve is that only two parts of the valve come in contact with the fluid being processed:
- The valve body
- The membrane or diaphragm
All other working components — such as the compressor — are isolated from the fluid flow path.
This isolation makes diaphragm valves suitable for use with many kinds of fluids and cleaning applications. The diaphragms can also be easily replaced or switched to a different diaphragm material if compatibility is an issue. In some cases, the compressor must be swapped out in order to switch diaphragm materials due to the different connection type of the diaphragms.
For highly sanitary processing applications, diaphragm valves are ideal, as there is nothing in the fluid flow path, and the valve may be easily sanitized and sterilized. In addition, their hygienic design complies with FDA, USDA, ASME BPE, and USP industry standards, allowing usage in stringent sanitary processing industries, including biopharmaceutical manufacturing.
Diaphragm valves also have outstanding self-draining characteristics and can purge process fluids from the valve when mounted in either horizontal or vertical orientations. These characteristics make diaphragm valves well-suited for use in highly sanitary processing applications where contamination from residual products or fluids may be an issue.
Features affecting drainability include:
- The valve size and tube specification
- The internal surface finish
- The drain orientation
- The surface tension/viscosity of the media
- The pipe run angle (generally recommended to be 2"-3")
The valve actuator (compressor) in diaphragm valves may be automated or operated by hand. Simple diaphragm valves are operated by hand with a lever or handwheel to move the compressor. Automated diaphragm valves may use pneumatic or electric actuators with devices such as solenoids, limit switches, and positioners to control valve operation.
Choosing a Diaphragm Valve
Hygienic diaphragm valves are made from various materials and can come with a variety of options.
- Most hygienic applications require the body material to be 300-grade stainless steel (primarily 316 or 316L). If more corrosion resistance is needed, alloys such as AL-6XN® and Hastelloy® C-22® are preferred and may even be required per specifications. In special cases, different types of plastic bodies may be required for extremely sterile “single use” applications.
- 2-way valves are available with forged or cast bodies. Forged bodies are much less porous than cast, which enables them to be polished to surface finishes as low as 10Ra. Block body valves are machined from wrought stainless steel barstock, which can also be highly polished.
- Surface finish and electropolish affects the cleanability and drainability of the valve. The lower the surface finish, the less likely there will be a bacterial contamination. Hygienic diaphragm valves must have at least a 30Ra-35Ra surface finish but some pharmaceutical applications require better. Surface finishes are available in 10Ra, 15Ra, 20Ra, and 25Ra. Electropolish is a chemical process that removes a thin layer of the stainless steel, thereby reducing surface roughness. It is available with all surface finishes better than 30Ra.
- Diaphragms are usually made from PTFE and EPDM, but in some cases Butyl, silicone, or Viton may be used.
- For hygienic diaphragm valve applications, butt weld or tri-clamp ends are typically used, although, other connection types may be available. Additional wall thicknesses and pipe schedule thicknesses may be supplied if needed.
- Diaphragm valves may be found in diameters ranging from 0.5" to 6". Note: Diaphragm valves used in non-hygienic industries may be found in diameters up to 14”.
Diaphragm Valve Advantages and Disadvantages
While diaphragm valves are suitable for use with a variety of fluids, they have trade-offs, like any other component.
Advantages
- Diaphragm valves are very easy to clean and maintain
- They contain few moving parts
- The diaphragm membrane and interior of the body are the only parts of the valve that come into contact with process fluids
- They are easily sterilized
- They feature an anti-leak seal with a tight shutoff
- Repairs to the valve may be made without interrupting other pipeline components
Disadvantages
There are some notable limitations to the use of diaphragm valves.
- Hygienic diaphragm valves can only be used under moderate operating temperatures (-40°F to 350°F) and pressures (≤ 150PSI)
- The body of diaphragm valves must be made from corrosion-resistant materials
Hygienic Diaphragm Valves for Flow Control Available from CSI
CSI is proud to offer hygienic diaphragm valves from ITT Engineered Valves, a premier supplier of industrial valves for mining, biopharmaceutical manufacturing, power, chemical, and other process-focused industries.
The EnviZion® valve is designed with the singular goal of reducing the overall cost of ownership. It requires no valve installation or diaphragm replacement tools and comes with no fasteners requiring regular re-torquing.
This design reduces diaphragm change times from an industry average of 23 minutes to only 3 minutes, an 87% reduction in maintenance time.
The EnviZion is engineered to improve cleanability by minimizing areas in the valve that can trap fluids and possibly lead to process contamination. In addition, the valve's active seating technology provides a reliable seal that does not degrade over time, unlike other diaphragm valve designs using passive seals.
The BioviZion® valve incorporates all of the EnviZion valve’s industry-leading technology into a small package designed specifically for the critical reliability needed for sampling and low-flow bioprocess applications.
The BioviZion stainless steel studs eliminate the small fasteners used in other compact diaphragm valves that are prone to galling and snapping.
Like the EnviZion valve, BioviZion's thermal compensation system applies sealing force only where needed. These features combine for a more reliable and less costly valve to operate and maintain.
CSI offers a variety of 2-way valves
Forged or cast 2-way valves are suitable for various applications. Incorporating valve bodies made with controlled sulfur 316L stainless steel, ITT’s 2-way valves meet the welding requirements of high-purity processing industries.
CSI can supply several types of integrated block valves
Block body valves can combine multiple valves into a single body, reducing total installation time and validation costs. In addition, the technology optimizes drainability and hold-up volumes and improves cleanability.
Finally, CSI can provide custom process fabrications for diaphragm valves consisting of multiple 2-way valves designed to fit a specific application
Compared to standard valves and fittings, these process fabrications will reduce hold-up volumes and improve drainability.
Next Steps
Diaphragm valves are one of the most versatile valve types used to control fluid flows, as processors may use them with a wide range of process materials. In addition, their design and ease of cleaning and sterilization make them particularly well-suited for use in highly sanitary process applications.
Not sure what type of diaphragm valve to use in your application? We're here to help. Call CSI at (417) 831-1411.
A Guide to Choosing the Right Valve
In determining the correct type of valve to use for your application, there are a number of considerations to take into account. This guide will help you make the correct choice for your specific need.
ABOUT CSI
Central States Industrial Equipment (CSI) is a leader in distribution of hygienic pipe, valves, fittings, pumps, heat exchangers, and MRO supplies for hygienic industrial processors, with four distribution facilities across the U.S. CSI also provides detail design and execution for hygienic process systems in the food, dairy, beverage, pharmaceutical, biotechnology, and personal care industries. Specializing in process piping, system start-ups, and cleaning systems, CSI leverages technology, intellectual property, and industry expertise to deliver solutions to processing problems. More information can be found at www.csidesigns.com.