[Illustration: FIG. 11.]
_a._ A safety or relief valve of the Ashton, Crosby, American, or
other make agreed upon in writing with this office, is to be regularly
included in the price, and is to be attached to each pump; preferably
extending horizontally inboard from base of air chamber, as shown in
Fig. 12, so that its hand-wheel for regulating pressure is within easy
reach. This hand-wheel must be marked very conspicuously as shown in
Fig. 11.
_b._ This valve is to be set ordinarily at a working pressure of 100
pounds to the square inch, and is to be of such capacity, that when set
at 100 pounds it can pass all the water discharged by the pump at full
speed, at a pump pressure not exceeding 125 pounds per square inch.
For 500-gallon pump a 3 inch valve.
For 750-gallon pump 3-1/2 inch valve.
For 1,000-gallon pump 4 inch valve.
For 1,500-gallon pump 5 inch valve.
The relief valve must discharge in a vertical downward direction into a
cone or funnel secured to the outlet of the valve. (See Art. 44.)
[Illustration: FIG. 12.]
The valve must be so attached to the delivery elbow and discharge cone
by flange connections as to permit of its ready removal for repairs
without disturbing the waste piping.