A hydrant is flow tested with a gauge and a nozzle, and the litres a minute go on a plate on the wall so the crew know what they have. One hydrant on a four inch main gives two thousand litres a minute, which that main cannot pass, and the water comes out warm in January, and the water company's own meter on the main shows no draw.
I am a firefighter with the hydrant testing duty, which is a van, a standpipe and a flow gauge.
How a hydrant is tested.
You fit the standpipe, open the hydrant into a nozzle with a pressure gauge, and read the static and the running pressure. The flow is worked out from the nozzle size and the running pressure. The main's size and the water company's data tell you what it should give, and a four inch main gives a few hundred litres a minute at best, which is why hydrants on small mains are marked as poor.
The number goes on the plate on the wall by the hydrant.
One hydrant, on a four inch main under a residential street, gives about two thousand litres a minute.
That is a big main's flow. A four inch main at the pressure in that street cannot pass it. It is not a matter of a good day: the pipe is physically too small for the water.
And the water comes out warm.
Not tepid. Warm, the way bath water is warm, in January, from a main that is buried a metre down in a street where every other hydrant runs at the temperature of the ground, which is a few degrees.
What has been checked.
The gauge. Two gauges, calibrated. The nozzle, measured.
The main. The water company has the drawings and it is four inch cast iron, laid in the 1920s, feeding a street of forty houses, and their engineer stood beside me while it ran and said it was not possible and did not say anything else for a while.
The company's meter. The street is metered as a district and the meter shows the draw of forty houses, and when the hydrant runs at two thousand a minute the district meter shows the draw of forty houses and nothing more.
The water is coming out of the hydrant. It is not going through the meter that everything in that street goes through.
The temperature.
I have put a thermometer in the flow. Thirty eight degrees, which is the temperature of a person.
I have had a sample tested. Mains water, chlorinated, potable, and the laboratory asked whether it had been heated before sampling and I said no.
Where the hydrant is.
Outside a house on a corner. The house is ordinary. The hydrant is old, with the old cast marker and the old plate, and the old plate, which I found under the new one when I changed it, had a number on it that was no flow rate but a date, in 1941, and the brigade's history for that date has this street on it, and a house on the corner, and a crew that could not get water because the main had been broken by the same thing that had broken the house.
What is done about it.
The plate says two thousand. It is true. A crew turning out to that street will have two thousand litres a minute from that hydrant, warm, from a main that cannot give it, and they will put a fire out with it, and I have decided that is the only fact on the plate that matters to them.
The water company have the test data and have written that the result is anomalous and that the main will be surveyed, and it has been, twice, and it is a four inch main.
What I do.
I test hydrants.
The one thing I have changed is that I test that one alone, and I do not put my hand in the flow.
The reason is the second test, when I did, to feel the temperature before the thermometer, and it was warm, and it was not the warmth of water. It had the give of something under the surface, the way a hand in a bath finds a limb, and I took my hand out and the flow ran on, clear, warm, at two thousand a minute, out of a main too small to carry it, until I shut it down.