The Pumping Engine House for Dock 8, Dock 9, Dock 10, and North Lock, was situated  on the north-eastern edge of Basin Number 4, the chimney, in its south-eastern corner, being outside the Shipwrights' Machine Shop number 81.  The Boiler House was on the southern side of the building.  It was almost level with Caissons H, J and K at the southern ends of the Dock 9, Dock 10 and North Lock respectively.

It was a brick building, with Portland stone facings and was distinctive in having a large water tank on the roof.  The foundations, chimney and superstructure were carried out as part of the main contract.  The constructional steel work was undertaken by Messrs Lysaght  and Company, of Bristol, under the supervision of Mr Harry Stanger, and after his death by his son, Mr W H Stanger.

The steam plant in the power-house consisted of ten cylindrical return tube boilers, each having a heating surface of 8,000 square feet, and a working pressure of 125 lbs.

There were two main pumps for emptying the three Docks and the North Lock.  The two pumps together were capable of emptying the largest of the Docks in four hours, discharging 120,000 tons of water.  The maximum height of lift of water from the bottom of the Docks to high water of ordinary spring tides was 53 feet.  In addition, there were two drainage pumps, each capable of delivering 1,500 tons of sea water per hour.  Each set consisted of three single-acting lift-pumps, with independent valve-boxes, worked from a three-throw crank-shaft, with the cranks at equal angles.  When the steam engine was working at the full speed of 90 revolutions per minute, the pumps were reduced by gearing to thirty double strokes per minute.  The pumps were manufactured by Messrs Easton, Anderson, and Goolden Limited.

The high-pressure cylinder of the steam engine was twelve inches in diameter, with the low-pressure one being twice that.  The stroke was 24 inches.

Compressed air was used throughout the North Yard Extension to operate Capstans, Penstocks, and the sliding Caissons to the Docks.  The air was compressed in two-stage, vertical compound air-compressors constructed by Messrs Fullerton, Hodgart and Barclay Limited, of Paisley.  They apparently carried works numbers 480 and 481.  The air cylinders were placed over the steam cylinders.  They were designed to deliver 18,000 cubic feet of air at 100 lbs pressure in thirty minutes when running at a maximum speed of 70 revolutions per minute.  The west engines pumped the reservoirs up to 100 lbs pressure in 11½ minutes, and the east engines in 13¾ minutes when running at 70 revolutions per minute.  The boiler pressure was 125 lbs per square inch and the steam pressure was 70 lbs per square inch.  A 16-feet diameter fly-wheel was mounted on the centre of the crank-shafts.

A patent Whitmore combined air-and-speed governor was fitted to the balanced throttle-valve.  It was designed to control the engine according to the amount of air required.  It was also designed to keep the engine running at its minimum speed when no air was required.  The air cylinders and valves were manufactured by Messrs Fraser and Chalmers Limited, of Erith.  The air generated by the compressors was delivered into a battery of six large receivers, made and erected by the Dockyard's own Engineering Department.  From there it is distributed throughout the Dockyard in 15-inch cast iron mains laid in subways built in to the upper part of all the Basin walls.

Further information is contained in the sections about the sliding Caissons and the hydraulic Capstans.