A diaphragm seal is a flexible membrane that contains fluid or gases to keep them in or out of a chamber while still allowing pressure effects to register. Such seals are used in a variety of settings where workers want to keep a fluid or gas isolated for safety, sanitation, or other reasons. Numerous companies manufacture them along with accompanying components. Often, the seal is available as part of a complete kit that includes mounting supplies, pressure sensors, and other accessories that go with the seal.

Materials used in diaphragm seal construction need to be strong, flexible, and durable. The seal may give considerably under pressure without cracking or rupturing, and it must be prepared for sudden spikes or drops in pressure that might create radical pressure differentials. If the seal is too flexible, it might be subject to breakage, while a stiff seal might be too brittle. In addition, some seals need to be able to cope with corrosive or harsh environments without pitting or melting.

One common use for a diaphragm seal is in a system used in food, pharmaceutical, or pure chemical production. In such systems, isolation and sanitation are critical for human health and end product quality. If fluids and gases leak around seals and into other components, they may become contaminated, and they can also soil the machine. Diaphragm seals are used on devices like milk pasteurization equipment to keep the contents contained as they move through the system.

These tools are also useful for pressure gauges. There are many environments where technicians need to know the operating pressure of their equipment, but they do not want to damage a gauge through direct contact with the contents. The pressure seal allows pressure changes to register in the far chamber, moving a pressure gauge without damaging it. This can allow such gauges to last longer and work more reliably.

Like other components of a pressurized system, a diaphragm seal requires regular inspection and maintenance. The seals can break down because of the contents of the system over time, and failures can be catastrophic if not caught early. It is usually possible to open seals to examine and replace them if necessary; in some cases the whole diaphragm seal unit, with the pressure gauge, diaphragm, and other components, may be removed. Workers may follow a checklist to rotate seal inspections and ensure that the entire system receives a thorough going-over periodically.