MACHINERY 



MACHINERY 



1957 



and the atmospheric pressure outside the cyhnder 

 forces the water up towiird the pUinger. 



One may swing a door open in one direction but it 

 closes tiplitly against the jamb in the other direction. 

 If a simihir arrangement, called a valve, is put at the 

 bottom of the cylinder, water can then enter but can 



4fi 





D r-ry 



^iz: 



-•Vol. 



2289. A, diagram of a simple pump; B, the clapper valve; C, 

 the poppet valve; D, the ball valve; £, an outside-packed pump; 

 F, an inside-packed pump. 



not run back and the water which enters the cylinder 

 is thus held. If a discharge-pipe is now placed at the 

 lower end of the cylinder, as shown in Fig. 2289, A, 

 and a valve placed in this which swings so that water 

 can flow out, but not into the cylinder,'our simple pump 

 will be completed. On the upward stroke of the 

 plunger one valve opens and the other closes; on the 

 downward stroke this action is reversed and the water 

 is driven out the discharge-pipe. 



The water from such a pump would come in spurts 

 with each stroke of the plunger. If an opening is made 

 in the bottom of an air-tight chamber, or tank, and this 

 connected with the discharge-pipe, we have a means of 

 preventing these spurts and maintaining a steady pres- 

 sure at the discharge. WTien the piston moves down- 

 ward and water is sent into the discharge-pipe, some of 

 it is forced up into this air-chamber, compressing the 

 air as it enters. WTien the plunger starts backward, 

 this compressed air can then expand and force out the 

 water. Thus, part of the time, water is leaving the 

 discharge directly from the push of the plunger and 

 part of the time from the expansion of the air in the 

 pressure-tank. 



There are three general types of valves: (1) The 

 clapper valve consists of a flat plate covering the valve 

 opening and hinged on one edge so as to swing in the 

 manner of a door (Fig. 2289, B). Frequently the face 

 of the plate is covered with nibber or leather. Except 

 in a few of the cheaper hand-pumps, this valve is not 

 found in modem spray-pumps. (2) The poppet valve is 

 one of the most widely usefl forms, especially on the 

 cheaper pumps. It consists of a flat plate with a tongue 

 projecting at right angles and acting as a guide to hold 

 the plate in place over the valve-opening (Figs. 2289, C, 

 and 2290). A flake of rust or a ijarticle of the spray 

 mixture is liable to catch under the plate and prevent 

 the valve from closing tightly. (3) The ball valve has a 

 metal ball resting on the round opening (Fig. 2289, I)). 

 The upward movement of the liquid raises the ball but 

 downward pressure only holds it more firmly in place. 

 Usually a cage is constructed over the ball to prevent 

 it from falling out of place. This type has generally 

 proved the most satisfactory. The constant shifting 



of the ball tends to grind the valve-seat smooth and 

 prevent any foreign particles from holding up the 

 valv(? off the seat. 



The air imjirisoned in the pressure-tank acts as a 

 spring to equalize the discharge. If the spray pulsates, 

 it shows that the t;mk is too small or that it has become 

 fillwi with water instead of air. Hand-pumps with a 

 relatively long time between strokes of the plunger 

 require a larger ijressure-tank than ilo power-pumps, 

 especially those having two and three cylinders. Most 

 tanks are cast-iron and are very heavy; also, with cast-- 

 iron, there is always danger that a thin place will give 

 way under pressure antl cause serious trouble. Sheet- 

 steel tanks are lighter anil better. All power-pumps and 

 many hand-pumps are supplied with a pressure-gauge. 

 This is usually attached to the pressure-tank. 



It is essential that a relief-valve be supplied since 

 most ijower-pinnps can easily be made to develop a pres- 

 sure too high for the pressure-tank and hose to stand 

 with safety. These valves are so constructed that they 

 may be set to act at any desireti pressure. The usual 

 type is a ball or poppet valve held in place by a power- 

 ful spring whose tension can be regulates] by a set- 

 screw. When the pressure of the liquid on the valve 

 becomes greater than the push of the spring, the valve 

 is raised and the liquid then passes back through a pipe 

 to the spray-tank. Such valves frequently cause trouble 

 by the uneven wearing of the valve or valve-seat and 

 the corrosion of the spring and working parts. 



A few pumps are now supplied with relief-valves so 

 arranged that when the valve is raised the pressure- 

 tank and discharge are cut off from the pump, and the 

 liquid leaving the pump flows freely back into the spray- 

 tank. This causes no wear on the relief-valve and, since 

 the pump does not have to work ;igainst pressure while 

 the valve is in action, it leads to a considerable saving 

 in power. 



If valves held without loss, and no material leaked 

 past the plunger-packing, the discharge of the pump 

 woidd be equal to the area of the piston-head multi- 

 plied by the length of the stroke. Valves always leak 

 back to a greater or less 

 extent and the packing is 

 seldom entirely tight, so 

 that the actual and theore- 

 tical discharge are not the 

 same. The difference be- p — ^ 

 tween the two is called p""^ 



IS 



This will 



xrc: 



the "slippage.' 



sometimes run as high as 50 L 



per cent when the valves t^J/ 

 are not fitting tightly. 



In using a hand-pump, 

 it is less tiring to make a 

 few strokes against heavy 

 resistance than to make 

 many strokes against a 

 lighter resistance. For this 

 reason pumps designed for 

 hand use should have rela- 

 tively large capacity. On 

 the other hand, large capii;- 

 city should not be ob- 

 tained by increasing the 

 diameter of the plunger 

 beyond a certain point. A 

 2-inch plunger when work- 

 ing against 100 pounds 

 pressure requires over 300 

 pounds of energy and even 

 with the well - pl.'inned 

 leverage of the long pumi>- 

 han<lle this is about the 

 maximum which may be 

 demanded of the man on 

 the handle. 



2290. Section of single-action 

 pump - cylinder showing poppet 

 valves and inside packing. 



