Under some conditions street pressure will not at all times of the day raise water to the highest floor which is intended to be supplied by city pressure. It then becomes necessary to use a device, known as a cut-off, by which tank pressure may be supplied to the floor. Fig. B shows the simplest form.
The two cold-water pressures are connected together, also the two hot-water pressures.
By opening the two upper valves and closing the two lower ones the floor may be provided with tank pressure, and vice versa. The objection to the use of this crude form of cut-off is that confusion may result from the use of valves.
In Fig. C a patented form of cut-off is shown, in which this trouble is not present. By throwing the lever up or down either tank or street pressure is turned on.