The Hawaiian gazette., 1885-06-10
Mcdonald Hydraulic Pressure Regulator.


DR.. J.. Mott Smith has kindly forwarded the fol
lowing account OF the Mcdonald Hydraulic Pres
sure Regulator. The remarks were made ut the
regular meeting Of the Louisiana Sugar Planters
Association, April 10th. The paper was read bv
Mr.. Dymond who said:
siE. PEEs1DNr:-In accordance with Your re-
quest, have prepared some more specific notes
concerning the Mcdonald hydraulic pressure reg
ulator for cane mills, concerning which made 4
few rewarks at our December meeting.
While this device has met with general favor
among our planters, believe its great merritt Is vet
scarcely appreciated. Its capacity for improving
the work of the most ordinary cane mill becomes
SO obvious after careful study of the case, that
We are led to wonder why the device was not sooner
discovered.
A few leading points in the expression of the
juice from sugar cane seem to be indIsputable:
J. The limit of the Capacity of a cane mill must
be the capacity! OF the engine under the steam
pressure used the momentum Of the hywheel the
strength of the gearing and Il III housings and the
diameter of the roller shafts
2. The usual pressure eNerted by the mill is all
that should be exertei by it, proper regard being
had for such contingencies of breakage as axperi-
euce scOws probable from any excess of pressure.
>. The ordinary steam engine depends entirely
upon the momentum Of its hy-wheel for the power
10 pass the dead centres.
l. The capicity of the ly-wheel is dependent
upon the weight of the rim and its speed and if at
the top and bottom centres 1t acquires Just enough
speed 10 enable 1t to pass the dead centres the ac
an excess of capacity in the fy-whee Is found
necessary TO induce regularity Of motion.
From these data We may then conclude thai an
engine built TO exert one hundred horse power
must exert that power when it passes the dead
centres and that when ii passes the top and bot
tom centres it gets impulses above the one hun
dred hOrse-p power then using, and If brought to q
sudden halt on the top or bottom centre, there
would be exerted at least two hundred horsepower
and with ordinary heavy hy-wheels three hundred
or four hundred horsepower; and hereiI. lies the
fertile cause Of cane mill breakages mill built
for one hundred horsepower is called upon TO re-
sist strain of two hundred to four hundred horse
power, ard il naturally gives way.
The late Mr.. L0ngacre, one Of the most accom-
pli5hed sugar-house engineers we have ever had IN
this STATE proposed, remedy for this, that our
cane mill engines should have double or triple
cylinders, and cranks and no tly-wheels, and then
the capacity of the cane mill to resist strains could
be calculated and never exceeded. This proposed
remedy would certainly have been effective, but
its considerable cost, the necessity for a new out
Mt, etc, prevented its application, and plan
tiers generally followed the old method, and ruin
Gus breakages of machinery occurred every season.
and still the expression of cane juice with single
mills fell under sixty per cent, and with double
mills under seventy per cent.
Daring all this time the question of slow running
and fast running mills excited considerable discus
sion. AID the conclusion seemed to be arrived at
that with given pressure the slower the speed the
greater the per centage of extraction but there be-
came evident also the following conclusion, viz:
That with given pressure the thinner the feed
the greater the per cenlsge Of extraction. Here
were embarrassing conclusions SLOW speed Civ
ing better extraction thaE fast speed. the cane
planter slowed his mil down, but found no I'M
provoment IN the extraction, and doubted the &C
suracy Of the theory overlooking the fact that to
accomplish his usual quantity Of work he had in