Crossness: Beam Engines
This page refers to the beam engines at Crossness Pumping Station.
Four beam engines were installed to pump raw sewage into the Thames on a falling tide.
The engines were originally built by James Watt and Co between 1862 and 1865. Each had a single cylinder of 48" bore and 9 ft stroke, with cam-operated drop valves. The engines worked at 11 rpm, and lifted 6 tons of sewage on each stroke. The flywheels are 28 ft diameter and weigh 52 tons. The rocking beams (photo 1) are 43 ft long, and originally lifted a group of eight 4 ft 6" diameter pump pistons working inside a 12 ft diameter casing. The steam engine was double acting, but the sewage pumps were single acting, so four pumps were disposed either side of the beam so that sewage was lifted on each stroke of the pistons.
Steam was originally provided by twelve Cornish boilers.
By 1897, additional pumping capacity was needed, and the beam engines were joined by four triple-expansion pumping engines installed in an adjacent building.
In the 1890s it was decided to upgrade the beam engines, and the work was eventually carried out by Benjamin Goodfellow and Co of Hyde, Cheshire, the contract being signed in 1899. They were converted from simple to triple expansion engines. This was a challenging undertaking within the constraints of the existing engines’ envelope.
The original steam cylinder was replaced by three new ones:-
- High pressure cylinder: 19 dia, 6 ft 10½" stroke.
- Intermediate pressure cylinder: 32" dia, 6 ft 10½" stroke.
- Low pressure cylinder: 44" dia, 9 ft stroke.
It will be noted that only the LP cylinder retained the original 9 ft stroke, being connected to the end of the beam, while the shorter stroke of the HP and IP cylinders reflects the fact that their piston rods were connected (in tandem) further inboard on the engine beam. The new tandem cylinders needed their own parallel motion linkage to guide their piston rod.
Steam was now admitted and exhausted by Corliss-type valves. The twelve Cornish boilers were replaced by ten Lancashire boilers rated at 150 psi.
Each of the two groups of 4 ft 6" dia sewage pumps was replaced by a single pump. The single pumps were 9 ft diameter, giving the same volume as the four 4 ft 6" dia pumps. In fact it seems that this alteration was made before the engines were upgraded, there being a reference to 9 ft diameter pumps in 1893[1]
The four original pump rods either side of the beam pivot had been connected to the outside of the beams by gudgeon pins passing through the beams. In the modified arrangement only one (larger) sewage pump rod was needed at each end, and this was connected in an ingenious manner. The existing gudgeon pin holes were used for new pins passing through a pair of cast iron 'flitch plates'. These resemble small versions of the main engine beams. Another pin passing through the centre of these flitch plates provided the connection for the new pump rod. A flitch plate be seen in photo 2, in the centre foreground. Immediately to its left is the red-painted crosshead of one of the sewage pump rods.
Another problem was posed by the need to connect the new tandem HP and IP piston rods to the beam, inboard of the LP piston connection. This was addressed by another, much larger flitch plate, the inboard end of which shared the outboard gudgeon pin of the pump's flitch plate. This is visible between the main beam plates in photo 3 and 6 (enlarged from photo 5). See also photo 11.
The 9 ft diameter pumps were of the bucket type, and the bottom of each new pump rod was connected to a bearing bracket bolted to the bottom of the bucket. See photo 12. The pump rods have been disconnected from the pumps, and provided with new guides.
Additional parallel motion linkage was provided to deal with the extra piston rods, and massive counterweights were added to the outer ends of the main beams to compensate for the weight of the extra pistons (see photos 8, 9, 10). Steam operated barring engines were installed to turn the flywheels to start the heavier main engines.
Much of the above information is drawn from 'Compounding the Crossness Beam Engines'[2]