the more successful of them are strictly of European origin.

High pressures and superheated steam puts valves with sliding surfaces, such as slide valves, piston, Corliss and gridiron valves out of business, for all of which a steam pressure of 150 lbs. per square inch and 50° of superheat is about the limit. The trouble with the higher pressures in connection with sliding surfaces is that the latter work very hard and require an excessive amount of

FIG. 40.-Poppet valve in two parts.

lubrication. Balanced valves are hard to keep tight under high-pressure steam. Superheat makes lubrication more difficult, besides it has a tendency to distort the castings on account of unequal expansion.

Poppet valves are usually of the double beat type, as shown in Fig. 39, for two reasons, first to reduce the lift and second to make them as nearly balanced as possible. A disadvantage of these valves is that the clearance is very large if they are located on the cylinder similarly to

Corliss valves. Some engine designers place them in the heads, this reduces the clearance, but makes trouble about getting at the inside of the cylinder. Another disadvantage connected with them is that the direction of the flow of the steam is changed several times, which results in a loss in pressure. They are not the ideal valves by any means, but for high pressure superheated steam we have nothing as yet which does the work better; they are subject to a great many evils and require close watching. The principal troubles seem to be leakage and hammer

FIG. 41.-Poppet valve with flexible ring.

ing. A change in the temperature of the steam will affect the valve sooner than the seat, it will expand more and commence to leak. To prevent this the steam valve is sometimes made in two parts, as shown in Fig. 40, in which an upper ring is fitted over the valve body and made to yield slightly in seating. Another way that gives good results is shown in Fig. 41, it consists in shrinking on a flexible steel ring which forms the upper seat; the ring will deflect under pressure and allow both lips of the valve to seat tight.

Hammering of poppet valves is generally prevented by cushioning on slow speed engines and by suitable cam

O

FIG. 42. Cam motion for poppet valve.

motions on higher speeds. A very effective motion of the latter kind is shown in Fig. 42, which makes the valve operate noiselessly at 250 revolutions and over.

CHAPTER III

PIPING AND SEPARATORS

Principle of natural drainage for piping. Supporting of pipe lines. Blowing out of pipe lines. Combination of separator and throttle. Ordinary steampiping is not safe for superheat. Pipe joints. Welded joint. Lap joint. Screwed and shrunk joints. Pipe-joint clamp for stopping leaks. Steam separators. Stratton separator. Separators with baffle plates and corrugations. Direct flow. Prof. Sweet's and vertical separators. Receiver separator for high pressure and superheat.

MANY accidents happen to the steam piping and throttle valves, which are caused by faulty design, construction or workmanship. The steam piping connecting boilers and engine must have ample provision for expansion and contraction; bends and elbows must be made to a long radius. Long and complicated steam pipes give poor economy. Natural drainage of the pipes is important; there should be no chance for water to collect in pockets. The principle of natural drainage is shown in Fig. 43. A shows valves and pipes arranged correctly. Water condensed in the pipe will either run back to the boiler or toward the engine. If it collects over the engine, it should be discharged through the drain pipe, which is usually opened to clear the pipe before the engine is started, or it will run into the cylinder and out through the exhaust when the cylinder is warmed up before starting. While the engine is running and taking steam, no water can accumulate in the vertical pipe.

42

View B shows the valve in an undesirable position near the boilers; there is a chance for water to collect

Valve

Valve

C

FIG. 43.-"A" shows a correct and "B" an incorrect stean main.

FIG. 44. No water can collect in the layout "A", if the drip valve is open; but "B" will collect condensate.

over the valve when closed, and on opening this would be thrown toward the engine, causing water-hammer.