Pressure Regulators

SOR Pressure Regulators are high performing instruments that are designed to provide reliable control of pressure in various stages of a flow system. The output pressure of a Pressure Regulator is sensed through a diaphragm, which in turn compresses or decompresses a spring. The compression of the spring determines whether the flow through the regulator will increase or decrease by moving a seat farther away or closer to the orifice.

SOR recognizes that there is no industry convention with respect to terminology and definitions pertinent to Pressure Regulators. This glossary applies to SOR Pressure Regulators.

Absolute Pressure (psia) – The sum of gauge pressure (psig) and atmospheric pressure (14.7 psi, 1.01 bar).

Absolute Viscosity – The ability of a fluid to resist flow, without accounting for the fluid’s density. Absolute viscosity is used in flow calculations and is the product of kinematic viscosity times the fluid’s density.

Atmospheric Pressure – The pressure that the atmosphere creates at a certain location (14.7 psi at sea level).

Bleed – When fluid moves from a higher pressure environment to a low pressure environment in a regulator pilot system.

Body – The protective casing that encapsulates the orifice and seat/plug.

Bonnet – The protective upper casing that encloses the force balancing mechanism and connects to the body.

Boost – A characteristic of the pressure regulator when the controlled pressure increases past the set point as the flow capacity increases towards its maximum value.

Compressibility – The ability of a fluid’s volume to change as a result of a pressure change.

Dead Band – The range that the supply pressure can be varied without initiating an observable response in the output.

Delta P (ΔP) – The change in pressure between the supply and output pressures. (Also known as pressure drop.)

Demand – The amount of fluid that is being required by a system downstream of the pressure regulator.

Density – The mass per unit volume of a substance.

Diaphragm – A flexible membrane that operates as the downstream pressure sensing element in a pressure regulator. The diaphragm works directly with the force-balancing mechanism that opens or closes the orifice.

Diaphragm Arm (Yoke) – A rigid piece that supports the seat block assembly and diaphragm.

Diaphragm Case – The supportive housing for the diaphragm that establishes an isolated pressure chamber.

Diaphragm Plate – A plate between the diaphragm and control spring that is used to evenly transmit the diaphragm force to the spring.

Disk – The movable, elastomer part used to adjust the flow rate through the orifice of the Pressure Regulator. (It is sometimes called the “seat”.)

Downstream – The part of a system that is beyond the Pressure Regulator (or any reference point) in the direction of the flow.

Drift – The change of a Pressure Regulator’s set point over time.

Droop – A characteristic of a regulator where the output pressure decreases past the set point when the flow through the regulator increases towards its maximum value.

Exhaust Capacity – The flow rate that Pressure Regulator with relief capabilities will vent at when the output pressure climbs above the set point.

Filter Regulator – A device that simultaneously filters and regulates the air that is passing through it. (Usually used to pneumatically control another device; like a Liquid Level Controller.)

Flow Capacity – The flow rate through a Pressure Regulator given specific inlet and outlet pressures.

Flow Coefficient (CV) – The liquid sizing coefficient for Control Valves and Pressure Regulators. It is defined as “the number of US gallons of water per minute at 60°F that will flow through a valve with a pressure drop of one psi”.

Flow Rate – The mass or volume of fluid that will flow in a specified unit of time. For volumetric flow rate, the standard English units are cubic foot per hour, while the SI units are cubic meter per hour. For mass flow rate, the standard English units are pounds per sec, and the SI units are kg per second.

Gauge Pressure (psig) – Pressure measured against atmospheric pressure.

Hysteresis – The difference between the output pressures of a Pressure Regulator when the inlet pressure is increased to a specific pressure above the set point, and then when the inlet pressure is decreased to that same set point.

Inlet – The connection between the regulator and the process where the media enters the regulator.

Kinematic Viscosity – Similar to absolute viscosity, kinematic viscosity is the tendency of a fluid to resist flow, except kinematic viscosity accounts for the density of that particular fluid.

(Kinematic viscosity = absolute viscosity/density)

NACE – National Association of Corrosion Engineers.

Natural Gas – Flammable gas, largely consists of methane and other hydrocarbons, occurs naturally underground.

Operating Media – The substance that is being regulated.

Orifice – The opening within the Pressure Regulator where the flow is choked/regulated by a seat or plug.

Outlet – The connection between the Pressure Regulator and the process where the media exits the regulator.

Output Pressure – The pressure immediately downstream of the Pressure Regulator.

Pneumatic – Containing or operated by air or gas under pressure.

Pressure Regulator – A valve that reduces the pressure in a flow line to a lower constant pressure. As the pressure downstream decreases, the regulator allows more flow through to increase the pressure. As the downstream pressure increases, the regulator allows less flow through to decrease the pressure.

Seat – The part of the seat body that contacts and seals the orifice when the Pressure Regulator cuts off flow. (Seats are usually made of an elastomer material.)

Sensitivity – The measure of how well a Pressure Regulator senses and reacts to pressure changes.

Set Point – The controlled pressure that the Pressure Regulator is set to output.

Sour Gas – Gas that is made up of a large percentage of sulfur or sulfuric compounds.

Specific Gravity – The weight of a particular volume of fluid in relation to the weight of an equal volume of the baseline liquid or gas, at the stated temperature. (The baseline fluid for liquid is water, and for gas is air.)

Spring Case Vent – The openings in the bonnet of the Pressure Regulator that allow the bonnet’s internal pressure to stabilize at the atmospheric pressure.

Supply Pressure – The pressure that is applied to the inlet and is then regulated.

Tapped Exhaust – The option where a Pressure Regulator’s exhaust vents are connected to piping that sends the exhausted fluid to a specified location.

Travel – The distance that the seat or plug moves between its fully open and fully closed positions.

Trim – The replaceable internal parts of the Pressure Regulator. (Diaphragms, gaskets, seat block assemblies, etc.)


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