Page:Steam engines; a thorough and practical presentation of modern steam engine practice (IA steamenginesthor00ludy).pdf/31

STEAM ENGINES 19 of all eccentric straps are about the same. Provision is made for lubrication by having an oil cup 11 cast with the strap. The eccentric 8 is mounted on the main shaft 9 and is held Eccensecure in the position desired by means of the set screw 12. trics for large engines are held by means of one or more set screws and a key.For a discussion of the function of the eccentric, the student is referred to the instruction book on "Valve Gears." Steam Chest. The box15, Fig. 8, containing the valve parts, is known

is

of the function of the eccentric, the

and

its

chest cover 16

is

by studs which pass through the flanges 17 into the The steam chest is connected to the steam supply by suitable

held in place box.

pipe

connections,

/ ™~^

steam being turned on

by

or off as desired

means

When

valve.

the

wM

into the chest through

V

valve,

it

Fig. 14.

^^te

J^ ^f

is

"

M K

j| M

ML

'M

§yK 4^L

the

into

where

cvlinder,

M

-.-—,-

itim

is

opened, steam passes

the

-

__

^ wff

of the throttle

throttle valve

Fig14 Typical Crosshead and Pin for Large Size Engine

expanded and then ejected through the exhaust opening.The energy of the steam is transmitted through the piston and piston rod to the crosshead 17, Fig.6,thence to the connecting rod 23, crank pin 33, to the main shaft.In order that these parts may properly perform the function of transmitting this energy, a correct design is highly essential; therefore, a discussion of their construction is deemed necessary.

Crosshead and Connecting Rod. The crosshead is usually made of steel which forms a connecting link between the piston rod and