Professor Moll on Mr Blanken's Fan-Gate Sluices. 99 



of a common sluice, when the difference of levels is somewhat 

 considerable. In this it may be effected without any difficul- 

 ty, by again rendering the pressure which the water exerts, 

 greater on D C and F G, than on D E and E F. For that 

 purpose, open the slides P, O, N, and keep Z and Z' shut ; 

 the water in the semicircular cases will descend to the level 

 of the river ; thus the hydrostatic pressure on the exterior side 

 of D C and F G, will become superior to that exerted by the 

 canal water on the gates D E and E F ; of course, the latter 

 will open even against a difference of level of several feet. 



It will now, I trust, be easily understood, how, by a similar 

 operation, the gates may be shut again, whilst the canal wa- 

 ters are running down through them. The slides P and O 

 are shut, and Z and Z' opened. The semicircular cases will 

 be again filled by the higher water from the canal, and the 

 difference of pressure, against both part of the fan-gates, will 

 determine the shutting of the gates. 



The velocity with which the gates are opened or shut, may be 

 managed at pleasure by those who guide the slides; and by open- 

 ing or shutting the slides more or less, according to the difference 

 of levels, a slow and gradual motion is effected. Even when 

 the fan-gates are in the act of shutting or opening, the opera- 

 tion may be reversed in an instant, and the gates either shut 

 or opened as occasion requires. 



It will also be understood, that the flood-gates A and B are 

 merely intended for passing vessels from one level to the other. 

 Whenever such passage is not wanted, the gates A B, may 

 be dispensed with. Accordingly, in the several inundation 

 sluices, which have been built lately, only one pair of fan- 

 doors is required. 



I hope it will appear from this description, that the fan-gates 

 may be opened and shut with ease and safety, whenever oc- 

 casion requires, and whatever is the difference of the levels. 

 When sluices, on the ordinary plan, are once opened, it is 

 impossible to shut them again whilst the water is running 

 through them, and, if once shut, as long as the exterior water 

 is somewhat higher than the interior, it is quite out of the 

 question to open the gates. In this country, at least, it is of 

 high importance to have the means of opening and shutting 



