Both diaphragm valves and globe valves are used to control the flow of liquids through a pipeline. Each has both advantages and disadvantages, particularly when looking at chemical resistant valves for use with the types of aggressive media that might be found in chemical processing applications. We take a look at both diaphragm and globe valves, consider their differences and offer some guidance on which might be the best solution for your specific application.
A Globe valve is a linear motion valve which is primarily designed to stop, start and regulate flow. A globe valve consists of a movable plug and a stationary seat in a spherical body. When the valve handle is turned the plug (or disc) is lowered or raised by means of the valve stem. When the disc is fully lowered, the fluid flow is shut off and when the disc is fully raised, the fluid flow is at its maximum rate. Variable flow rates proportional to the opening size are also possible with globe valves. Manual globe valves tend to have a threaded stem with a handwheel to open and close it using a screw motion, whereas automated globe valves generally have smooth stems and are controlled through an actuator. The sealing surface is resilient, meaning that it withstands wear very well and provides both good sealing properties and a long service life. This means that globe valves are a good solution for applications with frequent operational requirements.
Advantages of globe valves:
- Their simple design means that they are easy to maintain and cost-effective to manufacture.
- They are quick to open and close, with an overall relatively low valve height and a short stroke.
- Ideal for smaller spaces.
- Suited to connections that require flanges.
- Good shut-off results.
- Resilient, with a long service life.
- Available in a variety of designs, each with a unique application in mind.
Disadvantages of globe valves:
- They can be difficult to open and close, and large valves require considerable power to do so.
- Heavier than other valves of similar pressure ratings.
- The direction of the media flow is limited.
A diaphragm valve consists of a valve body (which has two or more ports), an elastomeric diaphragm and a weir or seat that the diaphragm presses on to close the valve. The elastomeric diaphragm is a versatile and dynamic seal, often constructed from a rubber or plastic moulded solution with an insert in either a metal or an engineering plastic. When the rubber diaphragm comes into contact with the seat at the top of the valve, a seal is formed. The seat of the valve comes in two different options: a straight-through design or a saddle design. The saddle design for the diaphragm valve has a weir effect and is more commonly used for chemical resistant valves because a bonnet over the diaphragm and control mechanism keeps the liquid contained, preventing leakage, as well as the saddle shape meaning that the valve is self-draining. Solenoid diaphragm valves are a popular solution, providing automated control of the opening and shutting of the solenoid diaphragm valve.
Advantages of diaphragm valves:
- A simple, cost-effective solution.
- The flow media only comes into contact with the diaphragm, protecting the valve from contamination.
- The seal is leak-proof thanks to the tight shut-off and the elastic nature of the diaphragm material.
- Suitable as a chemical resistant valve as it copes well with corrosive fluids.
Disadvantages of diaphragm valves:
- Not ideal for larger pipe diameters.
- Poor pressure resistance.
- Suitable only for moderate temperatures.
Applications for globe valves and diaphragm valves
Globe valves lend themselves to use in applications where fast action, leak tightness, maintenance and safety are major concerns. They can be used in water treatment, chemical production, oil and gas transport and almost any valve application where pressure drop is not an issue.
Diaphragm solenoid valves are ideally suited to corrosive applications, where the body and diaphragm materials can be chosen for chemical compatibility. Diaphragm valves are also well-suited to abrasive applications, where the body lining can be designed to withstand abrasion and the diaphragm can be easily replaced once worn out.
MGA Controls offers a wide range of both globe valves and diaphragm solenoid valves suited to industries such as pharmaceutical where both the media flow and the cleaning media can be corrosive. The MGA Controls’ range of chemical resistant valves is stocked from the leading manufacturers of globe valves and diaphragm valves. If you would like further advice on which option would be most suitable for your requirements, whether it’s a globe valve, a diaphragm valve or one of our many other solutions, find out more about your options on our dedicated chemical resistant valve page.