Triple-expansion engines

The Sir William Prescott and Lady Bessie Prescott engines are known as inverted marine type triple-expansion steam engines. They were built by Worthington Simpson in Newark-on-Trent and named after the chairman of the Metropolitan Water Board and his wife. The engines were installed to each pump 12 to 19 million gallons of drinking water per day to reservoirs in North & East London.

The engines stand 62 feet tall and weigh 800 tons. They have a top speed of 25.4 revolutions per minute and generate 1008 water horsepower.  Each engine has three double acting cylinders known as the high, intermediate and low pressure cylinders. Each measures 29, 54 and 86 inch respectively.  In service days, steam entered the high pressure cylinder at 200 pounds per square inch. This has been reduced to 60 psi for operation in preservation.  Steam is reused by the remaining two cylinders before being exhausted into a separate condenser which produces a vacuum.

The crank webs are set 120 degrees apart providing smooth balanced operation to the engine motion and a steady discharge from the pumps into the water mains.  There is no point in the engines’ rotation where no pump is delivering water.

The triples were commissioned in 1929 and ceased operating in 1980.

Engines Nos. 6 & 7 are mirror images of one another.

Technical Details

Name Sir William Prescott Engine & Lady Bessie Prescott Engine
Built 1928
Commissioned 1929
Engine Maker Worthington Simpson Ltd. (Newark-on-Trent)
Steel Castings & Forgings William Beardmore & Co. (Glasgow)
Cost  (pair) £94,000
Height 62 Feet
Length 45 Feet
Weight 800 Tons
Top Speed 25.4 RPM
Steam Pressure 200 PSI (Superheated)
H.P. Cylinder Dia. 29 Inch
I.P.  Cylinder Dia. 54 Inch
L.P. Cylinder Dia. 86 Inch
Stroke 5 Foot 6 Inch
Steam Guarantee 9.875 lb Per Pump Horse-Power Per Hour
Valve Gear Poppet Type With Variable Cam Timing
Crank Setting 120 Degrees
Flywheel Weight (2) 32 Tons Each
Flywheel Diameter (2) 17 Feet
Pumps (3) Compound Single Acting Ram Plungers
Pump Diameters 25 1/2 Inch  & 30 1/2 Inch
Maximum Pump Output 19 Million Gallons Per Day
Maximum Pump Pressure 400 Foot Head
Capacity 12 Million Gallons Daily @ 400 Foot Head
  16 Million Gallons Daily @ 300 Foot Head
  19 Million Gallons Daily @ 200 Foot Head
Displacement Per Revolution 521 Gallons (Compound)
  364 Gallons (Single)

 

Technical Details

Name Sir William Prescott Engine & Lady Bessie Prescott Engine
Built 1928
Commissioned 1929
Engine Maker Worthington Simpson Ltd. (Newark-on-Trent)
Steel Castings & Forgings William Beardmore & Co. (Glasgow)
Cost  (pair) £94,000
Height 62 Feet
Length 45 Feet
Weight 800 Tons
Top Speed 25.4 RPM
Steam Pressure 200 PSI (Superheated)
H.P. Cylinder Dia. 29 Inch
I.P.  Cylinder Dia. 54 Inch
L.P. Cylinder Dia. 86 Inch
Stroke 5 Foot 6 Inch
Steam Guarantee 9.875 lb Per Pump Horse-Power Per Hour
Valve Gear Poppet Type With Variable Cam Timing
Crank Setting 120 Degrees
Flywheel Weight (2) 32 Tons Each
Flywheel Diameter (2) 17 Feet
Pumps (3) Compound Single Acting Ram Plungers
Pump Diameters 25 1/2 Inch  & 30 1/2 Inch
Maximum Pump Output 19 Million Gallons Per Day
Maximum Pump Pressure 400 Foot Head
Capacity 12 Million Gallons Daily @ 400 Foot Head
  16 Million Gallons Daily @ 300 Foot Head
  19 Million Gallons Daily @ 200 Foot Head
Displacement Per Revolution 521 Gallons (Compound)
  364 Gallons (Single)