The Trent Severn Waterway Lock # 21

How the Peterborough and Kirkfield Lift Locks work.

The Peterborough Lift Lock on The Trent Severn Waterway was opened in July, 1904. It transfers boats, up and down in a single lift of 65 feet (19.8 m).

Peterbrough Hydraulic Lift Lock , 65 foot lift.

Needed Data (English Units of Measure):

  • Boat chamber size: 140 ft by 33 ft by 7 ft deep (holds the boats)
  • Piston Rod: 7.5 feet in Diameter (holds the chambers up and moves up and down)
  • Lift: 65 ft (the distance the chamber is raised or lowered)
  • Weight of water: 1 cubic foot of water weight 62.43 pounds (may be a fluid or a water soluble fluid mixed in)
  • The Upper Chamber is filled with 7 feet of water depth and the Lower Chamber with 6 feet of depth.
  • A boat displaces it's own weight in water, Principle of Flotation. The number, weight or size of boats in either chamber will not impact the operation.
  • Path of Least Resistance is what moves the lower unit up and allows the upper unit to descend.


  • Piston Rod travel (65+65) = 130 feet (65 ft out of the cylinder and 65 ft into the cylinder).
  • You need to keep some of the Piston Rod in the Cylinder at the top of the stroke plus some room at the bottom of the Cylinder to accommodate that.
  • The side guides supports the Chambers from breaking free so the Piston Rods add an extra safety feature assisting the Side Guides to achieve that result.
  • The bottom of the cylinder would require some extra footage so the Piston Rod at all times is well within the cylinder and not bottomed out.
  • The overall height would be approximately that of a 12 story building were it all above ground.


  • Upper Chamber Water Fill: 140 x 33 x 7 = 32,340 Cubic Feet or 915.8 Cubic Meters
  • Lower Chamber Water Fill: 140 x 33 x 6 = 27,720 Cubic Feet or 784.9 Cubic Meters
  • Weight of the water (Upper Chamber): 32,340 x 62.43 = 2,018,986.2 pounds or 915,796.7 Kg
  • Weight of the water (Lower Chamber): 27,720 x 62.43 = 1,730,559.6 pounds or 784,968.6 Kg
  • 2,018,986.2 pounds = 901.3 imperial tones or 1,009.5 US tons or 915.8 metric tons
  • Area of the Piston Rod = Area of a circle at the bottomof the pisotn rod on The Trent Severn Waterway = 3.14 x 3.75 x 3.75 = 44.2 square feet (pi times radius squared)
  • The Upper Chamber's Pressure is: 2,018,986.2/44.2 = 45,678 pounds per square foot or 317.21 PSI or 2,187.09 kPa
  • The Lower Chamber's Pressure is: 1,730,559.6/44.2 = 39,152 pounds per square foot or 271.89 PSI or 1,874.62 kPa
  • What this all boils down to is (317.21 psi - 271.89 psi) = 45.32 psi lifts the lower unit

In the sketch, I have shown the piston rod as a half a sphere at the bottom. This creates 2 times the surface area of a flat circle having the same diameter. The water pressure surrounding the rod, if in fact that is the actual design, will act as a minor resistance to travel and the upward push happens on the sphere. Area of a Sphere is, Area of a sphere at the bottomof the pisotn rod on The Trent Severn Waterway , four multiplied by pi and then multiplied by the radius squared, finally divided by 2 because only half is used.

Opening the valve between the two cylinders lets the heavier boat chamber, which is at the top of its stroke, descend. That in turn, increases the pressure in both cylinders forcing the lighter boat chamber, which is at the bottom of its stroke, up. Rapids and drops within the rivers are bypassed in order to navigate between the previous and next lock. The principle is the same for the other locks, which can vary from Conventional Locks, Flight Locks, Marine Railroads or Lift Locks. The goal to go smoothly from points A to B is met.

Pressure attempts to push the water out of the cylinders by finding the "Path of Least Resistance". The cylinders are sealed so the water cannot escape and the system cannot allow the pressure to exceed the Design Limit. Both are resolved as the lighter chamber moves up resulting in equalized pressure throughout. Opening the connecting valve between the two cylinders allows the water and pressure to flow from the unit at the top of its stroke to the unit at the bottom. When the full stroke is completed, the valve closed, the water level in the unit moving down will have stopped one foot above the level of the Trent Canal and the unit moving up will have stopped one foot below the level of the Trent Canal. Water is then added or released, as needed, so the gates can open and boats can transfer in our out starting the process over again. A very simple set of principles used in an extreme situation due to the size and weight involved.

Many scenarios of worst case can be considered. Short of a total traumatic failure in the structure the worst I can think of happening is that one of the stationary holding gates at the top fails and opens, flooding the entire chamber beneath with more than the designed foot of extra water resulting in exceeding system’s Design Limit for pressure, breeching either cylinder or, most likely the connecting pipe between the cylinders. That in itself could create a number of events to occur none with a happy ending..

Lock #21, Peterborough's Hydraulic Lift Lock, built from 1896 to 1904. A magnificent achievement even by today's standards and tools available.

Disclaimer: This document is theoretically correct but the sizes may vary slightly in actuality, as the Government agencies never seem to publish data that is useful in this kind of document. It may be out by inches or a foot but it is all we could find at the time of creating the document. In industry I had a rule: "you cannot be promoted till you can be replaced so pass on your knowledge, correctly and faithfully, so others can follow you smoothly and with minimal disruption."

Flight locks are locks joined together, like steps, to allow for a higher lift, just like a Lift Lock but not as efficient.

The other Locks are simply two sets of doors that open and close so when the chamber is filled with water the upper doors open so vessels can move in or out. Closed, to allow the water to be pumped out to the water level at the lower chamber, then those doors open and the vessels can move in or out.

Brief History of The Trent-Severn Waterway

The start to finish time line spans eighty-seven years with the systems construction starting in 1833 at Bobcaygeon and finishing in 1920 at Port Severn, three hundred and eighty-seven kilometers from Lake Ontario.
The Navigation channel runs a depth of six feet from start to finish. The locks vary in raising the water level some exceptions are; flight locks, the Big Chute Marine Railway with a lift of eighteen meters (58 feet), the Kirkfield Lift Lock with an average lift of fifteen meters (49 feet) and the Peterborough Lift Lock (finished in 1904) with a lift of twenty meters (65 feet).
Peaking at Balsam Lake at 180 meters (600 feet) above Lake Ontario and 80 meters (250 feet) above Lake Huron’s, Georgian Bay.
Standard lock dimensions are one hundred and twenty feet long by thirty-two feet wide. The three exceptions are the lock 21, lock 44, the Big Chute Marine Railway at one hundred feet long by twenty-four feet wide and lock 21 is slightly larger, lock 45 at Port Severn is only eight-four feet long and twenty-three feet wide setting the limit if you wish to traverse The Trent Severn Waterway from one end to the other.

Setch of Lock 21, Peterborough on The Trent Severn Waaterway
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