The Beam Pump

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.

Hydraulic Ram Pumps

Two Ram Pumps are installed at Coultershaw. These very clever devices can pump water to height of more than 300m using only water as the power source. Invented by the Montgolfier Brothers in the late 1700s they have been widely used throughout the world to pump drinking water and provide irrigation.

The foreground pump was donated by the National Trust from a site at Waggoners Wells, near Hindhead, and is belived to date from the 1930s. This pump is fed from the base of the fountain and can be seen on open days pumping water to a spout at the top of the Pump House. The larger pump came from the nearby Chingford pond.

Ram Pumps - How they work

The hydraulic ram pumps water without using any external power. It only needs flowing water to operate and can pump water uphill for long distances.

How does it work?

1. Here water flows down the inclined drive pipe from the base of the fountain into the body of the ram pump.

2. As the flow through the waste valve increases, water pressure closes the waste valve suddenly.

3. The closure induces a pulse of high pressure in the pump body, which opens the delivery valve and a small amount of water – about 10% of the flow – enters the air vessel.

4. The pressure in the pump body then falls, the delivery valve closes and the waste valve reopens. This sequence repeats regularly, perhaps 50 times a minute.

5. The water forced into the air vessel compresses the air, which pushes the water out through the delivery pipe. The water can be pumped into a remote storage tank, or as at Coultershaw, to a discharge pipe from the roof of the Pump House.

Archimedes Screw

In 2012, with support from the Leconfield Estate, the Coultershaw Trust installed a 16.5 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.

Energy generation and river level data can be found on the Hydro Generator page


There have been mills at Coultershaw from before the Domesday survey of 1086, until 1973 when the last mill was demolished. The mills were located here on the River Rother so that they could be powered by river water.  Coultershaw had a variety of mills over the centuries- corn mills, fulling mills and malting mills.

At the time of the Domesday survey, carried out by King William the Conqueror 1086, a mill at Coultershaw was valued at an annual rent of 26 shillings and a bucket of eels. The Domesday survey recorded 5,624 water-powered corn mills in the country, one for every 300 inhabitants.   Local farmers brought their grain to the mill to be ground into flour, with the miller receiving a proportion of the flour produced as payment for his work.  Flour was produced by grinding grain between heavy horizontal stones powered by a waterwheel.

A variety of milling activities were carried out in the Coultershaw area, in number of mills rented by a number of different millers. In 1240 there may a have been a fulling mill here, which was used to prepare woollen cloth. By 1534, there were a malting mill and two corn mills on the site, and by 1666 there were three corn mills.

In 1907, John Gwillim, who already operated Fittleworth Mill and the North Mill at Midhurst, took a lease on Coultershaw Mill from the Petworth Estate. He modernised the mill replacing the grind stones and wooden machinery with steel shafting and rollers to grind the grain more efficiently. As John Gwillim operated the three watermills on the River Rother, he was able to control the flow of water to operate his mills in the most efficient way.


In 1923, the mill was destroyed by fire, and was rebuilt within 12 months, in steel and ferroconcrete.  A garage was added to the east side, with a concrete and steel floor over the top of the Beam Pump.

John Gwillim died in 1929 and the business was continued by his son, Gordon. The mill was severely damaged by fire in 1946, but was repaired and continued in production. Gordon Gwillim died in 1970, and his widow Dorothy continued the business until it closed in October 1972 and the mill was demolished.