Oil Trades Pump School

Welcome to Oil Trades Pump School! This is a 100% free online learning tool brought to you by Oil Trades Supply Corp and our various partners which will continuously grow and be updated live! Please click on animations for more information, check out the equations and tables below for specific information on how to make pumping calculations and also the properties of various products as they relate to the pumping industry.

Internal Gear Pump


External Gear Pump


Lobe Pump


Vane Pump


Animations Courtesy of Our Friends @ PumpSchool.com

Formulas for Reciprocating Pumps

I have a reciprocating pump and I know what my max rated rod load is (in foot pounds). I also know what PSI I need. What size plungers do I need?
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I have a pump with no tags or specifications on it. How do I find out what Gallons Per Minute (GPM) this pump is capable of?
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I have a reciprocating pump and I know what my max rated rod load is (in foot pounds). I also know what size plunger size my pump has. What PSI will my pump produce?
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I know what maximum PSI and maximum GPM I need. What size pump do I need?
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Formulas for Centrifugal Pumps

I know what maximum PSI and maximum GPM I need. What size pump do I need?
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How do I calculate PSI (Pressure in Pounds Per Square Inch) or TDH (Total Dynamic Head)?
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How do I calculate Brake Horsepower Required for a centrifugal pump?
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General Equations & Conversions

TermFormula / Conversion
PSI.434 x head-feet x specific gravity
(1) Barrel42 Gallons
Gallons Per Minute (GPM)Barrels per Day * .0292
Horsepower (HP)Torque/lbs/inch x RPM / 63,025
1 US Liquid Gallon231 cubic inches
1 US Liquid Gallon.13368 cubic feet
1 US Liquid Gallon3.78541
1 Cubic Foot7.84 US Liquid Gallons
1 Cubic Foot28.31685 Liters


Chart of Relative Density / Specific Gravity for Common Liquids

Specific Gravity is used when sizing a centrifugal pump. Liquids with a specific gravity greater than 1.0 are heavier than water and conversely, liquids with a specific gravity lower than 1.0 are lighter weight than water and will generally float on water.

MaterialDegrees CelciusDegrees FarenheitSpecific Gravity
Alcohol, ethyl (ethanol)25770.787
Alcohol, methyl (methanol)25770.791
Alcohol, propyl25770.802
Butane, liquid25770.601
Crude Oil, CA15.56600.918
Crude Oil, MX15.56600.976
Crude Oil, TX15.56600.876
Ethylene glycol25771.1
Gasoline, Natural15.56600.713
Gasoline, Vehicle15.56600.739
Water, pure439.21
Water, sea/salt25771.025
Centrifugal Pump Formula:
Minimum Horsepower Required = ((Max GPM) X (Max PSI) / 1710) / (Efficiency in Percentage) X (Specific Gravity of Material)
Assuming you have one measurement for your pump but not the other:
PSI = TDH / 2.31
TDH = PSI X 2.31
Brake Horsepower Required = GPM Required X (Total Dynamic Head) / 3940 / Efficiency
Min. Plunger Size Needed = Square Root of (Rod Load Rating of Pump / Max. PSI / 3.142)
Max. PSI = Rod Load Rating of Pump / (Plunger Radius X Plunger Radius X 3.142)
(Plunger Radius X Plunger Radius X 3.142) = Sq. Inches of Circle
(Sq. Inches of Circle) X (Stroke Length) X (Number of Plungers) = Cubic Inches of Liquid Per Revolution
Cubic Inches of Liquid Per Revolution / 231 = Gallons Per Revolution
(Gallons Per Revolution) X (Max RPM) = Gallons Per Minute

NOTE: Max RPM in the above equation varies according to type of pump, size of stroke, and other variables. Duplex pumps often run about 100 RPM Max. while triplex pumps will run somewhere between 100 RPM Max and 400 RPM Max.

Reciprocating Pump Formula:
Minimum Horsepower Required = (Max GPM) X (Max PSI) / 1550

Internal Gear Pumps



How Internal Gear Pumps Work:

Internal Gear Pumps Consist Of One Gear Inside Of Another Gear Where The Liquid Product Travels Between The Two Gears

  • – Liquid product enters the suction port between the rotor (larger yellow gear) and the idler (smaller white gear) teeth.
  • – Liquid product travels through the pump via the ‘gear-within-a-gear’ principle. The idler (smaller white gear) is offset to create a larger internal volume on the bottom, below the idler, (see animation above) and the liquid is transferred through the pump and out through the discharge port
  • – The locked pockets between the idler and the rotor assures consistent volume control as the liquid moves through the pump head.
  • – It is essential that the rotor and idler teeth mesh perfectly at the top of the casing to form a complete seal equidistant from the discharge and suction ports.

External Gear Pumps



How External Gear Pumps Work:

External Gear Pumps consist of two gears side-by-side with a seal created between them with Liquid Product flowing around them.

  • – Liquid Product travels on the ‘outside’ of the gears between the internal casing and the teeth.
  • – The seal (and therefore suction) is created in the middle, between the two gears
  • – Finally, after travelling around the gears, the Liquid Product is forced through the discharge port.

Lobe Pumps



How Lobe Pumps Work:

Lobe Pumps Use The Principles of Expanding and Contracting Interior Space to Pump Liquid Product through the Pump Head

  • – First, the Rotating Lobes create an expanding volume on the inlet side of the pump
  • – Next, as the lobes rotate, the Liquid product is forced between the grooves of the lobe and the inside of the casing
  • – As the lobes continue to rotate the volume on the inlet side contracts while the volume on the discharge side expands and the Liquid product is forced through the discharge port

Vane Pumps




How Vane Pumps Work

Vane Pumps Consist of a slotted rotor mounted at the internal wall of the casing so that a crescent shape is formed – the crescent shape creates more pull through the pump head. Inside each ‘slot’ there is a retractable blade that slides in and out ‘sweeping’ the Liquid Product through the pump to the discharge port.

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