Hydraulic water lifts have of late years been used to elevate water by water-pres sure. With them va rious arrangements of piping to suit a wide scope of conditions are possible. If city water pressure does not reach the upper floors, the pressure on the lower floor may be employed to lift the supply for the upper floors, either for direct use from the pipe as usual, by aid of a closed accumulator, or by first delivering the water elevated into an open tank and then piping as in the ordinary tank installation. The power-water of a lift (that used to elevate with) is not wasted as in the case of a ram. The service for the low-level fixtures is simply carried through the power cylinder of the lift, and elevation takes place only during the use of faucets connected to the street pressure. The amount of water elevated is therefore governed by consumption on the lower floors; and the ratio of amount elevated to that used directly from the initial pressure, is as the capacity of the power cylinder to that of the one operated by it. An approximate estimation of the relative amounts of elevated and initial supply needed, must, on this account, be made before a lift of proper construction can be selected.
Cistern water can also be lifted by this method to either an open or closed tank, using or wasting the power water according to circum stances. In Fig. 68 is shown a plan by which the use of hard city water, useful for some purposes, is made to pump rain water for baths, trays, etc., by means of a water lift.
Domestic supply by what is termed the Pneumatic System, is a feature of modern plumbing in many isolated buildings. The manner of pumping, though it may be accomplished by any of the means mentioned, is usually by hand pump. Instead of the open elevated
tank supplying the fixtures by gravity, a closed tank capable of with standing the required pressure is placed either in the cellar or in the ground. The pump is connected with the tank at the bottom, with a check-valve between the pump and tank. The house service is also taken from the bottom of the tank. Pumping the water in, crowds the air in the tank into the upper portion, so that, by the time the tank is three-quarters filled with water, there is in the neighborhood of four atmospheres' (or 45 pounds') pressure on the gauge. Part of the storage tank being occupied by air, and much of the water in It not available under the pressure thus established, higher pressures are often employed, either by pumping air in with a separate pump, or by use of a pump delivering both water and air. The former is the more satisfactory.
A type of pneumatic service apparatus is shown in Fig. 69. The good features of these systems are that cheap and permanent sepport for the tank is secured; the water is kept cool in summer and free of frost in winter; and, if sufficient capacity is provided, fire-pressure for a time can be obtained. The disadvantages are that plain iron cylinders injure the water; galvanized cylinders are costly; large cylinders are hard to make and keep air-tight through the strain of transportation and installation; calking seams is expensive; a battery of small cylinders offer numerous seams and connective joints as chances for leakage, and only a fraction of the water is available under ordinary pressure; high pressure is severe on the pump and parts; and hand pumping is very laborious. Pressure higher than necessary for the purpose, is useless expense in any system.