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Glossary of Pressure Regulator Terminologies (P-Z)


Partial Pressure – In any gas mixture, the total pressure is equal to the sum of the pressure (partial) which each gas would exert were it alone in the volume occupied by the mixture.

Parts Per Million (PPM) – A convenient means for expressing low concentrations. As applied to gases, PPM stands for moles per million moles. PPM by weight is expressed as pounds per million Pounds. PPM by volume is usually expressed in cubic feet per million cubic feet.

PCV – Abbreviation used in flow charts and means Pressure Control Valve. Usually has reference to a Self-Contained Pressure Regulator.

Physical Hazard – Descriptive of a chemical for which there is scientifically valid evidence that it is a combustible liquid, a compressed gas, explosive, flammable, an organic peroxide, an oxidizer, pyrophoric, unstable reactive or water reactive.

Poison – A substance that in relatively small doses has an action, when it is ingested by, injected into, inhaled or absorbed by, or applied to a living organism, that either destroys life or impairs seriously the function of one or more organs or tissues.

Polar– A molecule that has an asymmetric distribution of positive and negative charges. (Nonpolar refers to a symmetric distribution of charges.)

Poppet – The valve plug that seats against the orifice to prevent passage from the high pressure side to the low pressure side.

Porting Configuration – A term which describes the location and flow path (high pressure or low pressure) of valve or regulator.

Pressure Transducer – A device that provides a liner D.C. voltage output proportional to the applied pressure.

Pressure Transmitter - A device that provides a linear ouput proportional to applied pressure.

Process Analyzer – A general class of instrumentation that is used to analyze conditions in process streams on a continuous basis.

Process Control Instrument – A combination instrument that is comprised of a Process Analyzer, which analyzes or monitors process conditions, coupled with a control section. This instrument puts out a control signal used to actuate changes of temperature pressure or feed rate of material.

Process Wetted – This term refers to the areas of the device that come into contact with the flow stream. This does not normally include the cap, range spring knob, etc.

Proof Pressure – A test pressure applied to control devices to verify structural integrity. No deformation or excessive leakage is permitted at this pressure and control element must function normally subsequent to this test. Normal industry standard is 1.5 times (150%) of working pressure. See also "Burst Pressure" and "Maximum Operating Pressure."

Pressure Vaporizing Regulator (PVR) or Vaporizing Pressure Regulator (VPR) - Abbreviations used in some flow charts.

Pyrophoric – The ability of a chemical to ignite spontaneously in air at a temperature of 130 deg. F or below.


Roughness Average (Ra) - The average difference between peak and valleys of a surface. Usually expressed in micro inches or micro meters.

Rare Gas – Refers to those constituents of air which comprise less than 1% of air and are generally considered inert such as argon, helium, krypton, neon and xenon.

Reference Mixture – A mixture with one or more properties that are sufficiently well-established to be used for the calibration of an instrument, the assessment of a measurement method or for the assignment of values to materials.

Reforming – The process of thermally or catalytically rearranging the molecules to produce a product of higher volatility and octane quality.

Relief Valve – A type of pressure relief device, designed to relieve excessive pressure, and to reclose and reseal to prevent further flow of gas from the cylinder after reseating pressure has been achieved.

Repeatability – The ability to reproduce output readings when the same pressure value is applied consecutively, under the same conditions, and in the same direction.


SCC/Min – Standard Cubic Centimeters Per Minute.

Self-Contained Pressure and Regulator – A pressure-regulating device wherein all elements of the mechanism are contained in one unit.

Self-Relieving (Self-Venting) – A feature incorporated in certain pressure-reducing regulators which enables the unit to relieve the outlet pressure when adjusted in the decrease direction.

Sensitizer – The ability of a chemical to cause a substantial proportion of exposed people or animals to develop an allergic reaction in normal tissue after repeated exposure to the chemical.

Servo-Regulator – A dome-operated pressure regulator with a sensing device which gives feedback information about the outlet pressure and automatically adjusts the dome pressure. This allows the regulator to provide large flows with minimal pressure drops.

Set Point – The control point desired for operation of a regulator.

Setability – A term used to describe the ability to adjust a hand-loaded pressure regulator to a specific set point. This involves the number of turns of rotation on the adjusting knob to reach the set point. It is sometimes referred to as resolution.

Single Stage Pressure Reducing Regulator – A regulator which reduces high pressure to low pressure and controls the low or outlet pressure with one stage of pressure reduction.

SLPM – Standard Liters Per Minute.

Socket Weld – A welding of two materials formed by placing one end within another end.

Solvent – A substance capable of dissolving another substance (solute) to form a uniformly dispersed mixture (solution) at the molecular or ionic size level.

Span Gas – Gases used as a reference point to "span" an analyzer.

Specific Gravity (Sp. Gr.) – The ratio of the weight of one substance compared to the weight of an equal volume of another substance which is used as a standard. Usually gases are compared to air (air = 1) while liquids and solids are compared to water (H2O = 1).

Specific Heat – Amount of heat required to raise a unit mass of a substance one degree of temperature at either constant pressure or constant volume. Usually expressed in Btu per pound per degree F.

Specific Heat Ratio – The ratio of specific heat at constant pressure to the specific heat at constant volume.

Specific Volume – The volume of a unit weight of a substance at a given temperature.

Stainless Steel – Alloy steels containing high percentages of chromium, from less than 10% to more than 25%.

Standard Temperature and Pressure (STP) – An internationally accepted reference base. Standard temperature is 0 deg. C. Standard pressure is one atmosphere or 14.6960 psia.

Sublimation – The direct passage of a substance from solid to vapor without appearing in the intermediate (liquid) state. An example is solid carbon dioxide (dry ice) which vaporizes at room temperature.

Supply Pressure Effect or Regulation Nonaccuracy – This is accuracy of the set pressure or outlet pressure with a change in the inlet pressure. In the case of a single stage regulator, 1% accuracy means 1 psi outlet change per 100 psi inlet change. This effect can be compensated for by using a two-stage regulator.

Surface Finish – The relative smoothness of a polished or nonpolished surface. Typically refers to a wetted area of a valve or regulator.


Temperature Coefficient (TEMPCO) - The percentage change of the outlet or controlled pressure with respect to the temperature of the device. It is usually expressed as psig change per degree Fahrenheit of temperature change.

Thermal Zero Shift – The zero shift due to changes of ambient temperature from room temperature to specified limits of the operating temperature range.

Tied-Diaphragm – A feature of certain regulators whereby the stem (poppet) is physically attached to the diaphragm. Thus, an increase of pressure at the low pressure side will pull the poppet closed.

Total Hydrocarbon Content (THC) – THC is used to describe the quantity of the hydrocarbon impurities present. Usually expressed as methane equivalents.

Toxic– The ability of a chemical substance to produce injury once it reaches a susceptible site in or on the body.

Triple Point (tp) – The definite temperature and pressure for a pure substance at which the three phases (solid, liquid and vapor) coexist in equilibrium as an invariant system.

Two-Stage Pressure Reducing Regulator – A regulator which reduces high pressure to low pressure and controls the low or outlet pressure with two stages of pressure reduction. Thus, the outlet of the first stage of regulation feeds the inlet of the second stage of regulation. Used when more stability of operation is required. See "Supply Pressure Effect."


United States Pharmacopoeia (USP) – The official publication for drug product standards.

Unstable Reactive – The ability of a chemical in the pure state, or as produced or transported, to vigorously polymerize, decompose, condense, or become self-reactive under conditions of shock, pressure or temperature.

Upstream Pressure – See "Inlet Pressure."


Vapor Pressure – The pressure characteristic at any given temperature of a vapor in equilibrium with its liquid or solid form.

VAR – Vacuum Arc Remelt. A double melted material where the first melt is typically done with an electric furnace and argon oxygen decarburizaton, then the material is remelted using an electric current under a vacuum. This tends to give a much cleaner product with better hot workability.

VIM – Vacuum Induction Melting. A process performed in an induction furnace in which the crucible and heating coil are enclosed in a vacuum chamber.


Water Reactive – The ability of a chemical to react with water to release a gas that is either flammable or presents a health hazard.

Working Pressure – See "Maximum Operating Pressure."


Zero Gas – Gases which are used as a reference point to "zero" an analyzer.