A defective vacuum, or loss of vacuum, may occur from the following causes:
1st. From the glands of the low pressure cylinder leaking.
2d. From the pet cock of the air pump being left open.
3d. From the joints of the connections about the condenser leaking.[65]
[65] To discover a leak about a condenser, pass an exposed light, as a candle, about the joints, etc., and where there is a leak the flame will be drawn in towards the condenser.
4th. From the condenser being cracked, and therefore leaky.
5th. From the injection cock or valve being closed.
6th. From the condenser tubes being foul for lack of being cleaned. From the L. P. cylinder escape valves or cylinder cocks being leaky, and therefore letting in air.
7th. From the slide valve and piston of the L. P. cylinder leaking.
8th. From the air pump valve being leaky or broken. From the circulating pump being defective, as from having leaky valves.