Gas pressure regulators are used to reduce the pressure of gas supplied from a high-pressure cylinder of gas to a workable level that can be safely used for operating equipment and instruments. There are two basic types of gas pressure regulators: single-stage and two-stage. Single-stage pressure regulators reduce the cylinder pressure to the delivery or outlet pressure in one step.
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Two-stage pressure regulators reduce the cylinder pressure to a working level in two steps. Since the performance of each is influenced by mechanical characteristics, the choice of gas regulator depends on the type of application for which it is intended.
The two most important parameters to be considered are droop and supply pressure effect.
Droop is the difference in delivery pressure between zero flow conditions and the gas regulator's maximum flow capacity. Supply pressure effect is the variation in delivery pressure as supply pressure decreases while the cylinder empties. For most regulators, a decrease in inlet pressure causes the delivery pressure to increase.
The effect of these differences on performance can be illustrated with some examples. For instance, when a centralized gas delivery system is supplying a number of different chromatographs, flow rates are apt to be fairly constant. Supply pressure variations, however, may be abrupt especially when automatic changeover manifolds are used. In this scenario, a two-stage regulator with a narrow accuracy envelope (supply pressure effect) and a relatively steep droop should be used to avoid a baseline shift on the chromatographs.
Single-stage and two-stage gas regulators have different droop characteristics and respond differently to changing supply pressure. The single-stage regulator shows little droop with varying flow rates, but a relatively large supply pressure effect. Conversely, the two-stage regulator shows a steeper slope in droop but only small supply pressure effects.
On the other hand, if gas is being used for a short duration instrument calibration, a single-stage gas regulator with a wide accuracy envelope (supply pressure effect) but a comparatively flat droop should be chosen. This will eliminate the need to allow the gas to flow at a constant rate before the calibration can be done.
The ideal construction for high-purity gas service is a gas regulator that has a stainless steel diaphragm. Such regulators are non-contaminating and assure satisfactory use for all applications of noncorrosive and mildly corrosive gases.
Regulators for corrosive gases must be selected from those recommended with each gas listing. A gas regulator equipped with a stainless steel diaphragm has several advantages over the elastomeric type. It does not outgas organic materials and it also prevents the diffusion of atmospheric oxygen into the carrier gas. Both Buna-N and Neoprene diaphragms are permeable to oxygen. The chemical potential of oxygen between the carrier gas and the atmosphere provides sufficient driving force for oxygen to intrude the carrier gas through a permeable diaphragm.
As some of you may prefer to watch rather than read, I've also produced a VIDEO on this subject.
A Single Stage Regulator takes Cylinder Pressure and reduces it down to an adjustable pressure output.
For example, in the case of an Oxygen Cylinder, the cylinder pressure of up to 300 bar ( psi) is reduced in a single step to the output of 0-4 bar (for example).
The main advantage of a Single Stage Regulator is price. Simply put, they're cheaper than Multi Stage Regulators.
The downside is Single Stage Regulators have a less stable output, especially at low pressure settings.
Where Single Stage Regulators are used for high output applications, it will be necessary to adjust the pressure from time to time. This is because as the cylinder pressure drops, the output pressure will creep up.
0-4 bar Oxygen Regulator (for example)A Multi Stage Regulator is a bit like having two Single Stage Regulators in one!
The first, non adjustable stage, reduces Cylinder Pressure to around 10 bar (can be up to 20 bar).
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The adjustable 2nd stage is used to deliver the output pressure required by the operator.
This means when you adjust the Regulator, you are only dropping the pressure from between 10 or 20 bar to your desired output pressure. Not up to 300 bar down to desired output pressure!
Multi Stage RegulatorMulti Stage Regulators offers two key advantages over Single Stage Regulators.
Reducing cylinder pressure in 2 steps results in greater output pressure stability and consistency. Stable, Consistent output pressure is especially important where a very low pressure is required ' very small flame torches for example.
Secondly, where high gas consumption is used, the delivery pressure is more consistent over the life of the cylinder. This is because as cylinder pressure drops, a Single Stage Regulator will gradually deliver a higher and higher gas pressure. This will necessitate regular adjustment to maintain delivery pressure.
A Multi Stage Regulator offers much more consistent output pressure because the depleting cylinder pressure has little effect on the adjustable second stage.
From the front, Single Stage and Multi Stage Regulators look very similar.
But you can see from the above image, a Multi Stage Regulator has the 1st Stage protruding from the rear. This is the most obvious visual difference between the two types!
If you need your Gas Regulators to be cheap, Single Stage Regulators are likely to be your best choice.
If consistency of delivery pressure during high gas consumption applications is important to you, Multi Stage Regulators are likely to be a better choice.
If you use micro torches (Model 'O' or Little Torch for example), the greater outlet pressure stability of Multi Stage Regulators will be a significant advantage for you.
I hope you found this blog article about the difference between Single Stage and Multi Stage Regulators useful.
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Graham
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