To Stenm Throttle 4Valve,

212

MODERN STEAM PRACTICE.

C, Lower weights.

d, Upper weights.

e, Spiral spring.

a, Accumulator orhydraulic cylinder.

b, Loaded piston.

Fig. 135.—Valve Regulator.

each stroke of the engine isalso an objection to the useof the stand pipe.

As a substitute for thesefall stand pipes, the follow-ing arrangement has beenadopted in the St. Peters-burg water-works, recentlycarried out by Messrs. R.Laidlaw & Son of Glasgow.A throttle valve or regulatoris placed so as to be con-trolled by the pressure ofthe water in the main. Thepressure acts through asmall accumulator or hy-draulic cylinder fitted with aloaded piston and attachedto the regulator. This loadedpiston, as it moves withthe varying pressure in themains, acts on the throttlevalve, and thus regulatesthe motion of the engines.A further arrangement wasmade whereby the steamwould be automatically andinstantaneously shut off ifany burst took place. Fig.135 shows the arrangementadopted. The lower weightsare slightly less than thepressure on the water piston,and thus the piston spindleis kept in contact with theupper weights; the steamvalve being then half open,any increase of pressure thuscauses the upper weightsto be raised and the spiral