Single stage cylinder regulators
Cylinder pressure regulators are a convenient and flexible way to withdraw gas from a cylinder. Single stage models are used when occasional gas consumption is required, for example calibration gas injection.
A single stage cylinder pressure regulator 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 "single stage" means that the pressure drop from the cylinder to the application takes place in one step. The alternative is to use a two stage pressure regulator, which is slightly bulkier and a little more expensive to purchase. The benefit of the single stage regulator is that it has a light weight for convenient handling and economical. The reason to upgrade to a two stage regulator would be to ensure a very 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 will creep up slightly over time in response to the falling cylinder gas pressure. Two stage pressure regulation largely avoids this issue.
Single stage specialty gases cylinder regulators are ideal for one-shot applications such as calibration gas mixture injection or the introduction of purge gases prior to the use of process gases. The operator is always present when the calibration or purging operation takes place and can adjust the pressure accordingly using the large knob on the front of the regulator. 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 detector gas or carrier gases.
Specialty gases regulators differ from industrial and medical gases regulators and the three 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.
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 there 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 very 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.
Chrome plated brass and stainless steel are the two material of construction options for the specialty gases cylinder regulator body. The internal components of the pressure regulators also differ when brass or stainless steel bodies are selected. Chrome plated brass is the more economical option and can be specified when non-corrosive gases are in use. Inert gases such as helium and argon are suitable for brass body regulators, additionally oxygen and flammable gases such as hydrogen can use this class of product. Stainless steel should be specified when the gas mixture contains traces of reactive components, such as a mixture of 500ppb sulphur dioxide in nitrogen, or when pure corrosive gases are being used.
In harsh environments such as offshore oil and gas operations, where the salt spray may come into contact with the cylinder regulator, it is recommended to specify stainless steel construction, even if the gases inside the regulator are inert. Pharmaceutical and food processing applications are also sensitive to the materials used in their operations and these industries often prefer to use stainless steel regulators for all types of application. If a cylinder pressure regulator is to be used for multiple purposes it might be advisable to invest in a stainless steel version because it will be able to also perform the role required of a chrome plated brass cylinder regulator. Making this substitution in the other direction is, however, not recommended.
Cylinder pressure regulators do exactly that: they regulate pressure. They 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 that the regulator must be removed when the cylinder is empty and fitted to a new full specialty gas cylinder. In applications where single stage regulators are used this is generally not a problem because the single stage regulator will most often be chosen for intermittent flow applications and where the end user is present. However, 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 slightly more 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.