[ 427 3 
CD reprefents the bignefs of the infide of the barrel. 
EFG is the body of the cock the outward fhell 
being pierced with 3 holes at equal diftances, and 
correfponding to the three dudts HH, II, KK , 
. whereof 
HH is the dudt, that goes to the bottom of the barrel. 
1 1 , the dudt, that communicates with the top of the 
barrel ; and 
KK is the duett, that pattes from the cock to the re- 
ceiver. 
LMN is the key, or folid part of the cock, move- 
able round in the fhell EFG. When the canal 
LM anfwers to the duetts HH and KK , the pump 
exhaufts, and the air is difcharged by the perfora- 
tion N. But the key LMN being turned till the 
canal LM anfwers to II and KK, the perforation 
N will then anfwer to HH ; and in this cafe the 
pump condenfes. Lattly, when N anfwers to KK, 
the air is then let in or difcharged from the receiver, 
as the circumftance requires. 
Fig. IV. 
Is the plan of the principal valve. 
AhCD reprefents the bladder fatten'd in 4 places, 
and ttretch’d over the 7 holes IK, formed into an 
hexagonal grating 5 which I fhall call the honey- 
comb. 
EFG II ttiews where the metal is a little protuberant, 
to hinder the pifton from ftriking againft the 
bladder. 
