Two-stage cylinder regulators

Product overview

The Spectrolab FM53 is a two-stage cylinder pressure regulator from our Spectron range. It may be fitted to the cylinder outlet valve to reduce the high pressure of the gas in the cylinder to a lower pressure suited for the application. The phrase two-stage means that the pressure drop from the cylinder to the application takes place in two separate steps.

Applications

The two-stage regulators are chosen when there is a continuous flow of gases or the equipment will be left running unattended, for example with the flow of instrumentation gases such as hydrogen and Zero Air for FID detector gas or helium and argon as gas chromatography carrier gases.

Technical considerations

The pressure regulator is fitted with two pressure gauges, one to indicate the contents in the gas cylinder and the other to indicate the downstream regulator outlet pressure. The outlet of the pressure regulator may additionally be fitted with a shut off valve or a more sensitive flow metering valve.

At the inlet to the cylinder pressure regulator is a stem with a nut, which may be firmly screwed onto the cylinder outlet valve to form a gas-tight connection. There are several possible nut types on the inlet stem and these correspond to the various different thread connections on the cylinder valve. It is important to only connect a cylinder regulator to the correct type of cylinder; otherwise damage to the cylinder outlet valve may take place. For this reason it may be necessary to have several different types of regulator available for use on different types of pure specialty gases or specialty gas mixtures.

Product selection

Specialty gases regulators differ from industrial and medical gases regulators and the three different categories should not be interchanged. The materials of construction inside each regulator are selected to be compatible with the gases that they are handling. For example, the pressure controlling diaphragm in a specialty gases regulator is made from stainless steel whereas the same component in an industrial regulator may be made from rubber. To protect the integrity of the high purity specialty gases or high precision specialty gas mixtures, it is essential to use metal parts in contact with the gas to avoid potential contamination. Additionally, the machining tolerances of the different regulators are different and these influence the leak rate within the regulator and from the regulator to the atmosphere. They also determine how much contamination from air will ingress into the regulator and contaminate the gas stream. Specialty gases regulators have the lowest leak rates and the highest precision machining tolerances.

Cylinder pressure regulators do exactly that: they regulate pressure. These differ from valves, which regulate flow. It is therefore common to use a flow control valve such as a needle valve after the pressure regulator to make fine adjustments to the specialty gas flow rate.

The use of a cylinder regulator means it must be removed when the cylinder is empty and fitted to a new full specialty gas cylinder. In applications where two-stage regulators are used, this may be a problem because the two stage regulator will most often be chosen for continuous flow applications. If a continuous flow of gas is required even when the cylinder is empty, then an automatic changeover panel should be selected. This device connects two or more cylinders to the panel and allows the gas flow to be switched from the cylinder that is almost empty to to a fresh cylinder without any flow interruption.

If a cylinder pressure regulator is to be used for multiple purposes, it would be advisable to invest in the two-stage regulator because it will be able to also perform the role required of a single-stage regulator. The opposite is, however, not the case.

Working to a tight budget

The alternative to a two-stage regulator such as the FM53 is a single-stage pressure regulator, such as the FM51, which is more compact and less expensive to purchase. The benefit of the two-stage regulator is that it produces a steady outlet pressure from the regulator throughout the life of the gas cylinder. When single-stage regulators are left with a continuous gas flow, the outlet pressure creeps up slightly over time in response to the falling cylinder gas pressure. Two-stage pressure regulation largely avoids this issue. Single-stage regulators are ideal for "one shot" applications where the user is present, such as the introduction of calibration gas mixtures.

Sitting between the FM51 and the FM53 in terms of both price and pressure stability performance is the SPECTROLAB FM52exact. It has a single-stage design with added pressure compensation to give it performance similar to a two-stage regulator. If you are working within a capped budget, it may be the ideal choice for your application.

It is important to know that adjusting a 200 Bar cylinder pressure to a very low pressure can only be achieved by FM52 and FM53 regulators. For instance, if you are adjusting outlet pressure between 1 Bar and 1.5 Bar, only FM53 can achieve this low pressure. For adjusting outlet pressure between 2 Bar and 4 Bar, FM52 or FM53 should be selected. For adjusting outlet pressure between 5 Bar and above, FM51, FM52 and FM53 are your available options.