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Glossary of Terms

Air Eliminator

Device used to eliminate or remove air entrained in the fluid stream before fluid measurement.  These devices help to improve measurement accuracy.

API Gravity

A measurement developed by the American Petroleum Institute to determine how heavy or light petroleum liquid is compared to water.  If the API gravity is greater than 10 it is lighter and floats on water.  If less than 10 it is heavier than water and will sink.  The correlation between Specific Gravity and the API gravity is:


Back Pressure Valve

Valve used to maintain a minimum pressure for the entire system.  This ensures proper meter operates above the vapor pressure of the fluid.  The valve also holds a constant pressure against the pump for a constant flow rate across the meter.

Barrel (BBL)

1 barrel = 42 U.S. Gallons measured at 60°F.
BS&W Probe and Monitor

An electronic component that determines the amount of Basic Sediment and Water (BS&W) of a system.  This device detects entrained water content in petroleum products.  The water changes the capacitive re-actance as a function of the conductivity (dielectric constant) of the petroleum product.  This component is responsible for maintaining the quality of the “Merchantable Oil” of the system.


Vapor bubble formation as a result of the pump suction pressure dropping below the vapor pressure of the liquid.  When this happens the liquid boils and vapor bubbles form at the eye of the propeller.  As the bubbles move radially outward with the through the impeller they encounter a high-pressure region.  At this point they collapse and send pressure waves outward.  These pressure waves have an erosive effect on the impeller and housing.  This effect is called cavitation erosion.

Charge Pump and Motor

An electrically mechanical fluid pump used to maintain a certain pressure throughout the system.

Check Valve

One-way valve that only allows flow in one direction.  These valves are used when it is desired to prevent flow in the opposite direction of the process flow.  The cracking pressure of a check valve is the minimum upstream pressure require for the valve to operate.

Control Panel

Panel used to house the electronics that control the operation of the system.

Design Pressure

The maximum pressure a system is designed to operate.

Design Temperature

The maximum temperature a system is designed to operate.

Discharge Temperature

Require outlet pressure to maintain a design flow rate

Divert Valve

3-Way valve used to divert flow to a waste (reject) line.  The valve is usually controlled by the BS&W monitor to maintain the quality of the oil flowing through the system is marketable.

Double Block and Bleed Valve

A valve used to seal off a pipeline for testing or maintenance.  The valve is constructed so that there are two seal mechanism and a provision for any fluid that may pass to drain through a bleed port.

Lease Automatic Custody Transfer (LACT)

A system providing automatic measurement, sampling, and transfer of oil from a lease location to a pipeline or other method of transfer.

Flow Meter

A device to measure the amount of fluid passing through a system.

Flow Rate

The amount of fluid that moves past a given point in a given time.  Units are typically Barrels per Hour (BPH) and Gallons per Minute (GPM).

Net Positive Suction Head (NPSH)

Energy available to supply liquid to a given destination.  The dimension is a measurement of length (ft of liquid) and represented as a head of liquid.

Net Positive Suction Head Available (NPSHa)

Absolute pressure available to a system.  The NPSHa needs to be greater than the NPSHr at all flow rates since NPSHr increases as the pump flow rate increases.

Net Positive Suction Head Required (NPSHr)

Required pressure for a piece of equipment to operate in a safe manner. 
Note:  Cavitation is prevented when the NPSHa > NPSHr.  A reasonable difference is 3ft.

Natural Gas Liquids (NGL)

Gas that is processed through a plant to separate the heavier hydrocarbon liquids from the natural gas stream.  These heavier hydrocarbon liquids (NGLs) traditionally have a higher value than the gaseous natural stream.


The force exerted by a fluid per unit area.

Pressure - Absolute PABS-sm1

The actual pressure at a given position. PABS-Formula

Pressure – Atmospheric PATM

Pressure the atmosphere exerts on objects; 14.7 PSI

Pressure – Gage PGAGE

The difference between absolute pressure and atmospheric pressure. PGAGE-Formula 

Pressure – Vacuum PVAC

Pressure below atmospheric pressure (14.7 PSI). PVAC-Formula

Pressure - Vapor

The partial pressure of the vapor in contact with the saturated liquid at a given temperature.  When the pressure in a liquid is reduced to less than the vapor pressure, the liquid may change phase suddenly and “flash” to vapor.  When the fluid is adjacent to a surface and collapse of vapor bubbles can cause serious damage by eroding the surface material.

Operating Pressure

The estimated pressure a system operates under normal system conditions.

Operating Temperature

The estimated temperature a system operates under normal system conditions.

Programmable Logic Controllers (PLC)

A digital computer used for automation of an electromechanical process.  They are designed for multiple inputs and outputs.

Prover Manifold

Manifold with 3 valves and two tees that are used to prove and calibrate the flow meter to ensure meter accuracy is maintained over time.


A probe used to retrieve a representative “sample” of the process fluid.  This sample is then stored in a sample container.  The combined contents of the sample container gather over a certain time period are used to represent the true value of the fluid metered for a given time period.  The contents will be used to determine the API Gravity and the total percentage BS&W.

Specific Gravity (S.G.)

The density of a substance relative to the density of a known substance.



Filtering mechanism used to remove liquid entrained debris to help prevent damage to the pump, meter, and other system components.

Supervisory Control and Data Acquisition (SCADA)

Systems used to monitor and control equipment .  These systems encompass the transfer of data between a SCADA central host computer and a number of Remote Terminal Units (RTUs) and/or Programmable Logic Controllers (PLCs), and the central host and the operator terminals.  SCADA systems gather information and transfer the information back to a central site, carry out any necessary analysis and control, and display the information in a logical and organized fashion.


An electronic device capable of sending and electronic signal of a measurement usually pressure or temperature or flow rates to a data collection point.


A fluids ability to resist deformation by shear or tensile stresses or a fluid’s resistance to flow.  Value is typically expressed in units of centipoises (cP)


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Customer Testimonial

“Valin Measurement Group drastically increases production measurement and reduces pressure drop through their LACT units.”

Eagle Ford Shale Asset Manager