By function

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Functional options

Valves come into four main categories for function:

• Check valves: designed for a unidirectional flow in a device. Low and immediate forward flow with little pressure drop and very good sealing performance in reverse flow direction.
• Venting valves: designed to open at a specific, predetermined, opening pressure and re-seal once system pressure drops. Can be used to vent air or liquids from vessels, tanks, or other systems, or keeping pressure in a system or vessel until a predetermined pressure is reached and then the valve opens to vent.
• Dispensing valves: designed to dispense (usually a liquid) into an atmospheric container, creating a clean, constant steam. Popular in filling equipment and household condiments bottles.
• Access valves: designed to provide access to a pressure system (such as the body or arteries), allowing instruments such as guidewires, catheters, or scopes to pass through the valve whist preventing leakages, and close when the instrument is withdrawn.