Axle Pump


Many locomotives have an axle-driven pump to replenish water in the boiler as it consumed, but rarely does the designer or owner know how much water is pumped. The pump is commonly driven from an eccentric on one of the driving axles. Crosshead pumps are also sometimes used, with the main piston rod extension used as the pump ram. What all these types of pumps have in common is:-

  1. they all feed water into the boiler
  2. they are all single acting (i.e. one pumping stoke per axle revolution)
  3. all are connected to the axle one way or another.

Pump Capacity calculation

Guess work is sometimes used to estimate the amount of water consumed by a moving steam locomotive, and sadly is common place, however it is possible to estimate the water consumption by calculation, and there is a capacity calculator in the article on injectors, and this can be used to calculate the capacity required to maintain boiler water level from the axle driven pump.

The calculations assume that the pump is single acting. If a double acting pump is used, change the number of rams to 2.

Capacity of Pump
Enter metric OR English values to find calculated capacity.
Equivalent values shown in grey boxes after calculation
No of Rams:
Bore: mm ins
Stroke: mm ins
Driving Wheel Dia: mm ins
Locomotive Speed: kmph mph
Pump Capacity: ? litre/min
or ? UK fluid oz/min
or ? UK pint/min

Note: Simple formulas using +-*/() may be entered if desired,
not just straight plain numbers.
(for example, say 2+(1/4) may be entered for 21/4 [=2.25])

Disclaimer. Note the accuracy of these calculations is not necessarily exact, and are displayed to only 3- or 4-digit accuracy, and figures calculated here may vary from actual results. Results to be used at you own risk. Calculator provided for guidance for your personal use only.