The Beam Pump used to pump water from the River Rother to Petworth. It is a very unusual design, using long beams to transfer the power from the waterwheel to the pump barrels.
The pump is believed to be the 1782 original, although the present crankshaft was cast in 1912. The long beams have been replaced from time to time.
The simple construction of the pump made it easy to operate and maintain without any specialist skills or equipment. Any spare parts could be made locally.
How does it work?
Water from the River Rother comes under the road in a culvert. Most of the water is used to operate the waterwheel, controlled by a vertical penstock- a gate raised by a rack and pinion mechanism.
There are three pump barrels, each containing a piston which pumps water on its down stroke. A seal between the piston and pump barrel is made by back-to-back leather plungers. The pump draws water from the main culvert through a ‘clack-valve’ (or flap valve) into the chamber on the upstroke. Pumping takes place on the down stroke. Water was pumped to Petworth, 1½ miles (2.4 km) away through a 3 in (7.6 cm) cast iron pipe, which still partially exists. A pressure of 75-80 psi (5.5 bar) was required to reach the town. The air vessel, added about 1830, reduces pressure fluctuations from the output from the three pump chambers by compressing air in the top half of the cylinder. The Beam Pump ceased pumping water to Petworth in 1960. It now supplies the fountain at a pressure of about 10 psi (0.7 bar) so that the pump may be seen working.
Why are the beams so long?
With its long beams this pump is unusual.
For the pump to work properly, each pump rod must move vertically up and down in its pump cylinder. If this does not happen, the pump rod will get stuck! Using a long beam is a simple way to make the pump rod move vertically.
Each beam is pivoted at one end with the other end connected to the pump rod. Powered by the waterwheel, the crankshaft and connecting rod move the beam up and down. The pump rod (attached to the outer free end of the beam) moves in a very shallow circle to produce an almost straight-line motion.
The longer the beams, the shallower the circular motion and the nearer the pump rods are to moving in a straight line. So the longer the beams, the better!
Beam Pump – facts and figures
Timber beams: 12 feet 6 inches (3.81 m) long, with a cross section of 8 inches by 3 inches (20.32 cm by 7.62 cm)
Wrought iron push rods: 6 feet 7 inches (2.00 m) long
Wrought iron pump rods: 8 feet 4 inches (2.54 m) long
The long beams provide an almost straight line pumping action with stroke of 13 inches (3.30cm)
Each (of the three pump) cylinders: 6½ inches (1.65 cm) diameter with a stroke of 13 inches (3.30 cm)
Each cylinder delivers a gallon (4.54 litres) of water on each stroke
The pump could deliver 20,000 gallons (91,000 litres) of water per day, requiring over 6,600 revolutions of the waterwheel at a speed of 9¼ revolutions per minute during a 12 hour day.
The pump delivered a 170 ft (52 m) head of water to Petworth House and town, 1½ miles away uphill at a pressure of 75- 80 pounds per square inch (5.5 bar)
To pump the water to Petworth, the waterwheel produced about 3 horse power; today about ⅓ horsepower is needed to produce the water spout.
In 2012, with support from the Leconfield Estate, the Coultershaw Trust installed a 15 kilowatt Archimedes screw turbine. It is located in one of the sluices that had once housed a turbine to provide power to the mill. It generates electricity from a sustainable source.
Over the years, the base of the sluices had been scoured away by the action of the flowing water. Before the turbine was installed, divers helped pump over 50 tonnes of concrete under the brick work to stabilise the structure.
The turbine normally operates 24 hours a day, with a servo-controlled gate regulating the amount of water flowing through it.