The parts of valve are as follows, 1, the body, 2, the plug, 3, the packing and lifting gland, 4, the lifting cam, 5, lock-nut, 6, two brass rings of equal size, with a special gasket between them—all as shown in the engravings.

The valve is operated with a wrench on the square of the plug. The lifting gland when adjusted is permanently held by a lock-nut. By releasing the lock-nut with the wrench and turning the gland to the left, the plug is lifted so that it will turn easily. When the lock-nut is moved up, the lifting cam (which couples the packing gland to the plug) can be pulled out; the gland is then free to be removed for repacking. In use the best method of handling is to open and close the valve slowly—never with a jerk.

Fig. 640.

The tendency toward higher pressure steam boiler installation has made apparent the need of a blow-off, like this one described, made of strong material and correct in principle; in fact the high steam pressures now carried have almost made a revolution in boiler appliances.

The Fig. [640] represents two valves applied to the end of a blow-off pipe. The valve next to the boiler is open at all times excepting when the operating valve, next to the sewer is to be attended to for repairs, etc.

The table below is intended to correspond with the letters to be seen in the illustration, Fig. [640].

Table.

Size
in
Inches		Diam.
of
Flange		Centre
to
Face		Centre
to
Bottom		Centre
to
Top		Centre
to
Bottom		Diam.
of Bolt
Circle		No.
of
Bolts		Diam.
of
Bolts		Thick.
of
Flange
ABCDEI
141⁄221⁄241⁄241⁄221⁄831⁄441⁄211⁄16
11⁄4523⁄451⁄851⁄421⁄233⁄441⁄2 3⁄4
11⁄2631⁄457⁄8623⁄441⁄245⁄8 13⁄16
261⁄233⁄4771⁄433⁄8545⁄8 7⁄8
21⁄271⁄241⁄481⁄485⁄8457⁄843⁄41
381⁄4591⁄21045⁄865⁄885⁄811⁄8

One cock of this pattern is usually employed, but to use two (as shown in the figure) is the best practice especially for high steam service.