Bilge pump

The still-intact aft bilge pump of the Swedish 17th century warship Vasa as seen from the upper gun deck.

A bilge pump is a water pump used to remove bilge water. Since fuel can be present in the bilge, electric bilge pumps are designed to not cause sparks. Electric bilge pumps are often fitted with float switches which turn on the pump when the bilge fills to a set level. Since bilge pumps can fail, use of a backup pump are often advised. The primary pump is normally located at the lowest point of the bilge, while the secondary pump would be located somewhat higher. This ensures that the secondary pump activates only when the primary pump is overwhelmed and keeps the secondary pump free of the debris in the bilge that tends to clog the primary pump.^[1]

Ancient bilge pumps, or force pumps as they’re commonly referred to, had a few common uses. Depending on where the pump was located in the hull of the ship, it could be used to suck in sea water into a live fish tank to preserve fish until the ship was docked and the fish ready to be sold. Another use of the force pump was to combat fires. Water could again, be sucked in through the bottom of the hull and jet streamed onto the blaze. Yet another suggested use for a force pump was to dispel water from a ship. The pump would be placed near the bottom of the hull so as to suction water out of the ship. Force pumps were not only used on ships, but on land as well. They could be used to bring water up from a well or to fill high placed tanks so that water could be pressure pumped from these tanks. These tanks were for household use and/or small scale irrigation. The force pump was portable and could therefore, as on ships, be used to battle fires.

Force pumps could be made of either wood or bronze. Based on ancient texts, it seems that bronze was the preferred material since it lasted longer and was more easily transported. Wood was easier to build, put together, and repair but was not as durable as bronze. Because these were high-value objects on ships, few are found in shipwrecks because they were likely recovered after the ship sank. Force pumps were fairly simple in their construction consisting of a cylinder, a piston, and a few valves. Water would fill the cylinder after which the piston would descend into the cylinder, causing the water to move to a higher placed pipe. The valve would close, locking the water into the higher pipe, and then propelling it in a jet stream.

References

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