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Pump Seal Repair

Written by Silence
Last updated on 2009-12-30

Pump leaks occur frequently in aging water guns, but they are easily repaired.


Lubrication of the pump plunger should be done first to improve the seal and reduce friction. Silicone lubricant is generally accepted, being easy to apply and very effective; it is generally available as a grease or as a spray. Either form will work. However, do not use petroleum jelly, other oil-based lubricants, or any spray lubricant that uses a petroleum as the aerosol propellant. Oil can degrade natural rubber over time, although synthetic rubbers like Buna-N (often used for O-rings) are more durable.

O-Ring Replacement

If lubrication does not fix the seal, replace the seal completely - the old one may be degraded, hardened, or may have stretched and loosened. If the water gun's pump uses an O-ring for the seal, you can remove the O-ring and use a replacement. O-rings are easily obtained from hardware stores (such as Lowes, Ace Hardware, and The Home Depot), plumbing stores (like Noland's or Ferguson), or online (from sites like McMaster-Carr, ThomasNet's directory of O-ring suppliers, O-Rings USA, etc.). O-rings are generally identified by a number on an universal scale that corresponds to a specific inner diameter (ID), outer diameter (OD), and thickness measurement.

If you can't take measurements of your pump tube, take the O-ring into a plumbing or hardware store and compare its size to those of the O-rings in stock. If an identical O-ring is available, buy and use the replacement directly.

Using lubricant and capitalizing on the elasticity of rubber, any O-ring in a range of suitable sizes may fit and form an effective seal. If the O-ring is too small, use electrical tape or some other type of spacer underneath the O-ring to increase the diameter. Selecting a significantly larger O-ring than ideal is usually not a wise choice, as there are few ways to ensure a tight seal.

Pump Rod Replacement

Homemade Pump Rods

Another option, and perhaps the only one for pumps that are shipped without O-ring seals, is to completely replace the pump rod that came with the stock gun. If you have the stock seal, find an O-ring with a similar OD. Then, find a wood or aluminum replacement pump rod with an OD slightly larger than the O-ring's ID. If you don't have the original seal, just use trial-and-error with O-ring and pump rod sizes until you find a seal that works.

To secure the O-ring in place, wrap electrical or duct tape around the rod on either side of it. You may also use glue or cut sections of plastic tubing as a more permanent option. Wrap tape underneath the O-ring if it is too small.

Commercial Pump Rods

If it is too tedious to construct a homemade replacement pump rod, salvaging one from another commercial water gun may be possible. Most water guns have pump tubes with a 1/2" ID, and thus their pump rods and seals are often exchangeable. A pump rod may be taken from a water gun that is weaker and seldom used, or from a soaker that is damaged and will not be otherwise repaired.

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