302

DETAILS OP SCREW ENGINES.

that each valve is worked by a separateeccentric.

Pig. 162.

V'/, '/"//////////y.y’A

MR. winter’s EXPANSION VALVE.

STEAM THROTTLE VALVES.

Independently of the slide and expansionvalves, the steam is intercepted beyond themby a third means, termed the throttle valves.This is a supplementary detail used only whenindependent regulation is requisite, such asstarting, stopping, and the boiler’s priming.The valve is a disc of metal enclosed in acasing of suitable form, as the Fig. 163represents—being similar to the practice ofMessrs. Penn. The valve swings at right

Pig. 163.

ORDINARY STEAM THROTTLE VALVE.

angles to open and close, and the movementis effected by levers. In the place of levers,however, Messrs. Maudslay prefer mitregearing, as represented by Fig. 164, to move

the disc. The same result can be attainedby a worm and wheel motion, and also by

Pig. 164.

MESSRS. MAUDSLAY S MITRE-OEAP. MOTION FOR THROTTLEVALVES.

spur gearing. It may be added that theaction of the handle determines the kind ofgear motion to be adopted for the valve.Excepting the valves under notice, Messrs.Maudslay have often used double .beat equili-brium valves, which are raised and loweredby levers, or any other mechanical meansequally certain.

PISTON ROD GUIDE BLOCKS.

In pages 50 and 51, the advantages of theslipper guide block are made obvious inrelation to the direction of the crank pin;and in page 53, a description is given ofMr. Humphrys’ single piston ro guide block,

Fig. 165.

MESSRS. HUMPHRYS’ SINGLE PISTON ROD GUIDE BLOCK.

now illustrated by Fig. 165. The block, asalready stated, is in halves, each portionbeing almost a duplicate of the other. The