Pressure Regulator Types for Industrial Gases

Pressure management of industrial gases is both vital for safe working and essential because of the high static pressures that are employed to store gases in cylinders for transport. High pressure cylinders supplied from gas producers may range in pressure depending on the size of the bottle and type of gas and this is often around 200bar but can be much higher.

These cylinders can be fitted to systems singly, in pairs or in large banks where high gas volumes or sustained delivery is crucial. Pressure regulators for high pressure cylinders are often referred to as first stage regulators as they take the 200-400bar static cylinder pressure and reduce it to a safer and more manageable level which could be between 5 and 50bar. In some cases it may be required to use a single regulator to deliver a lower pressure such as for diving equipment or breathing apparatus and in which case, a dual stage regulator is needed. This unit combines a first stage regulator with a second stage unit to deliver two steps of reduction and the only adjustment is the final delivered pressure. The intermediate pressure between stages is fixed.

First stage regulators often fit directly to the high pressure cylinders using mounting threads that are specific to certain gases or gas types. These thread types may conform to one of several international standards such as UNI 11144, DIN 477, CGA V0-1 or NF E29-650. For example:

• UNI 11144 No.1H for Hydrogen (H2) or Methane (CH4)
• UNI 11144 No.2 for Carbon Dioxide (CO2) or Oxygen (O2)
• UNI 11144 No.5 for Nitrogen (N2)
• UNI 11144 No.6 for Air
• UNI 11144 No.7 for Acetylene (C2H2)
• UNI 11144 No.8 for Helium (He) or Argon (Ar)
• UNI 11144 No.9 for Nitrous Oxide (N2O)

Conventional G (BSPP) or NPT threads may also be used in certain applications or where cylinders have been connected to a high pressure manifold.

Since industrial gases are often used in critical processes and the high pressure cylinder fill volume is limited, it is often good practice to employ 2 separate cylinders or cylinder banks with a dual inlet regulator to make it easier to swap between supply sides when the supply pressure falls below a suitable minimum. Auto changeover regulators simplify this further by allowing the user to designate a primary supply side and then switch to the secondary side as the primary pressure reaches a minimum setpoint pressure. Alarms can be triggered at this point to alert the user that one supply side is exhausted and needs to be swapped before the other depletes.

Second stage regulators or intermediate pressure regulators take the reduced pressure from the first stage of up to 50bar and regulate down to the desired working pressure, anything between 1.5 and 50bar. These are the most common types of pressure reducing valves seen on sites and have to deliver accurate regulation for a wide range of desired pressures.

First and second stage regulators can often be used for liquids such as water or hydraulic oil subject to slight design variation or elastomer choice.

Third stage regulators are essential when very low pressures are needed as the second stage regulators are not sensitive enough when the desired pressure is between a few mbar and 1bar(g). Much larger diameter diaphragms are employed which makes third stage regulators easier to recognise from a distance. These regulators are most often for air or gas use only as the need for liquid pressure management at these pressures is not common.

What information do I need to select the correct Gas or Liquid Pressure Regulator?

Media

For common gases and liquids, it is often sufficient to name the fluid and note the fluid temperature range. For viscous liquids or solutions of several chemicals, the solution strength, percentage composition, viscosity and specific gravity would need to be considered.

Pressure

The maximum inlet pressure and the adjustable outlet pressure range are the key items. Where a particular flow rate has to be met, the normal working inlet pressure would help when sizing a valve for the flow.

Flow

If you need to achieve a specific flow rate, this must be communicated clearly so that the valve can be sized accordingly. Often a smaller valve than the line it is mounted in can be used to meet he requirement but consider if a larger unit would be better when nearing the flow capacity for a given inlet/outlet pressure combination.

Connections

The inlet and outlet connections may or may not be matching so confirming the type of joint - threaded, flanged, clamp etc with the relevant standard - BSP, NPT, PN16, PN40, ANSI 150RF, ANSI 300RF, ASME BPE etc and the size in inches or metric DN is key to ensuring the new regulator fits without issues. Regulators fitting directly to high pressure cylinders have other ranges of standard connections as mentioned earlier.

Materials

Do you have a specific material requirement to match a site standard or prevent corrosion? Most regulators can have choices between aluminium, brass or 316 stainless steel but other materials may be available too. The elastomer choice may be determined by both compatibility with the media and also the working and ambient temperature ranges.

Environment

Ambient temperature, direct sunlight temperature, corrosive atmosphere, wet or subject to water spray, indoor and outdoor environments all can impact the correct specification and it is always important to include these factors when known.

Certification

Compliance with safety and legislation is vital for plant operations, especially in explosion risk areas where ATEX, IECEx or EAC-Ex certification would be required. Other popular options are EC1935/2004 Food Safe or WRAS.

Do I need a relieving or non-relieving pressure regulator?

Relieving regulators are common for compressed air duty as they promote easy adjustment when lowering the downstream pressure. As the downstream pressure exceeds the setpoint as it is being lowered, a relieving regulator will vent the excess pressure to atmosphere until it matches the setpoint again.

Non-relieving regulators can only reduce the downstream pressure below the previous setpoint at the rate of consumption of the fluid. If there is no flow, the downstream pressure will not fall to meet the reduced setpoint until sufficient fluid has moved to allow the pressure to fall to and below the new setpoint.

Relieving regulators can be used on liquids, toxic or combustible gases only when the relief port is threaded to allow the piping of the vented fluid to a safe receptacle. If the relief port is not threaded to allow this, either choose a regulator that does have a threaded relief or go with a non-relieving one.