Most laboratory gas users will have to use some equipment to control pressure and/or flow rate. Pressure regulators will usually be central to the safe delivery of the gas.
Regulators prevent system over pressurisation when valves are closed down-stream of supply. Regulators can be single-stage or two-stage. A single-stage regulator will accept a high variable inlet pressure and allow adjustment of a lower steady outlet pressure. Unfortunately in the case of permanent and dissolved gases, single-stage regulators can exhibit a tendency to rising outlet pressure as the cylinder they are connected to empties.
As the cylinder empties the regulator valve spring pushes the valve further open. If a steady outlet pressure is needed this can be at least troublesome. Liquefied gases have less tendency to this problem as the singe stage regulator accepts vapour pressure which varies with ambient temperature not cylinder contents.
Consequently two stage regulators are favoured for:
- Steady outlet pressure
- Finer control over outlet pressure
These benefits are achieved by having two regulators joined in series within one piece of equipment. Tied diaphragm means that as the user closes the regulator down a positive (rather than passive) force is exerted automatically on the valve, ensuring positive shut-off.
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