DRAIN TAP - WATER
Drain Tap - Water
These Water Drain Taps were used on a number of vehicles to make it easier to drain coolant from the block or
radiator. Despite the convenience, the design of the unit has always been plagued with leakage problems. The sealing
mechanism uses two matching tapers; a tapered valve which rotates inside a tapered hole in a fixed valve body. The
design incorporates a spring to preload the rotating valve to ensure good contact between the two tapered surfaces.
Larger versions of this valve made from wood have been used for hundreds of years to dispense fluids from barrels and
casks. Being larger and made of wood, they work well because the tapered surfaces can be “hand-lapped” together
to achieve a very close fit. In use, the wood will swell as it absorbs some of the liquid, and that helps sealing the valve.
Scaling the design down and making it in brass created a very appealing drain tap, but that appeal is offset by the
annoying tendency to leak. We tried buying them, and they leaked. We tried making them ourselves, and they leaked.
We tried tweaking the design and some still leaked. Despite our best efforts, it has not been possible to match the
two tapers with enough precision to prevent leakage. Why can’t we fix these? We are hemmed in by two fundamental
requirements. First, these valves have to look as close to the original parts as possible. If that were not the case,
we would make a totally reliable, leak-free drain tap using modern ball valve technology. Second, the cost has to be
reasonable or no one would buy them. That means hand-lapping the mating parts until you achieve the perfect fit
required for a leak-free drain tap is not an option – the cost would be too high. These constraints and the inherent
challenges of the two mating tapers design have forced us to take an unusual approach.