TEMPLATE
the cylinder picked out,
we can choose a pump.
whether we want a
positive or non-positive
displacement pump.
complicated.
in our case.
continue putting out max
flow even through the hard
work of splitting a log.
would never do that.
out max flow as soon
as the work got hard.
likes a quitter!
pump, on the other hand,
pushes flow through the
system at a steady rate...
high resistance.
Perfect, right?
is: what kind of positive
displacement pump to use.
how to choose the
best positive displacement
pump for our system?
but a simple process of
elimination will allow us
to pick the right one.
we need a fixed or variable
positive displacement pump.
Table of Contents
Fixed Displacement Pump.......... pg.2-4
Variable Displacement Pump.......... pg.5-8
Notes:
Fixed Displacement Pump: Does not have a
control to change its displacement. As long
as it's receiving enough fluid, it always
displaces the same amount. Can only
displace more fluid by spinning faster.
Variable Displacement Pump: Can control its
displacement without having to change how
fast it spins. Best for cases where you
need nuanced speed control.
Fixed or Variable?
For this simple system, we don’t need to change
the speed at which we split logs. We might want to
restrict flow if we want to slow down the log
splitting a bit, but beyond that it's more or less
“put log in, hit go”.
So our system can operate on a steady flow rate
and we don’t ever need to change the pump
displacement. Which of the following types should
we pick?
a fixed displacement pump.
should do the trick.
Let's see if we can find
one in our catalogue.
of them. How do
we choose?
our cylinder to extend and
retract.
fast do we want to
split these logs?
Frank?
thinking.
the right speed: not so
fast that it'll be unsafe
for the cylinder, but still
fast enough to give us
an edge on Frank.
0.38 CID/rpm
hydraulic gear
pump 3/4" keyed
shaft CW
$142
0.5 CID/rpm
hydraulic gear
pump 3/4" keyed
shaft CW
$146
0.61 CID/rpm
hydraulic gear
pump 3/4" keyed
shaft CW
$150
Notes:
Frank's machine takes 12.1 seconds to fully extend and 8.9 seconds to fully retract. Let's see if we
can find something a little faster, while still picking the cheapest option.
A higher CID = higher cylinder speed.
0.38 CID Pump
Things We Know:
1. Pump GPM
CID x RPM ÷ 231 = GPM
GPM = gpm
2. Find hp
GPM x Pressure ÷ 1714 = hp
hp = hp
3a. Cylinder Extend Volume
𝛑 x (Cylinder Bore ÷ 2)2 x Stroke = Extend Volume
Extend Volume = inches3
3b. Cylinder Extend Speed
(60 x Extend Volume) ÷ (231 x GPM) = Extend Speed
Extend Speed = sec.
**faster than 12.1 seconds = good
4a. Cylinder Retract Volume
Extend Volume — (𝛑 x (Rod Diameter ÷ 2)2 x Stroke) = Retract Volume
Retract Volume = inches3
4b. Cylinder Retract Speed
(60 x Retract Volume) ÷ (231 x GPM) = Retract Speed
Retract Speed = sec.
**faster than 8.9 seconds = good
0.50 CID Pump
Things We Know:
1. Pump GPM
CID x RPM ÷ 231 = GPM
GPM = gpm
2. Find hp
GPM x Pressure ÷ 1714 = hp
hp = hp
3a. Cylinder Extend Volume
𝛑 x (Cylinder Bore ÷ 2)2 x Stroke = Extend Volume
Extend Volume = 192.33 inches3
3b. Cylinder Extend Speed
(60 x Extend Volume) ÷ (231 x GPM) = Extend Speed
Extend Speed = sec.
**faster than 12.1 seconds = good
4a. Cylinder Retract Volume
Extend Volume — (𝛑 x (Rod Diameter ÷ 2)2 x Stroke) = Retract Volume
Retract Volume = 144.25 inches3
4b. Cylinder Retract Speed
(60 x Retract Volume) ÷ (231 x GPM) = Retract Speed
Retract Speed = sec.
**faster than 8.9 seconds = good
0.61 CID Pump
Things We Know:
1. Pump GPM
CID x RPM ÷ 231 = GPM
GPM = gpm
2. Find hp
GPM x Pressure ÷ 1714 = hp
hp = hp
3a. Cylinder Extend Volume
𝛑 x (Cylinder Bore ÷ 2)2 x Stroke = Extend Volume
Extend Volume = 192.33 inches3
3b. Cylinder Extend Speed
(60 x Extend Volume) ÷ (231 x GPM) = Extend Speed
Extend Speed = sec.
**faster than 12.1 seconds = good
4a. Cylinder Retract Volume
Extend Volume — (𝛑 x (Rod Diameter ÷ 2)2 x Stroke) = Retract Volume
Retract Volume = 144.25 inches3
4b. Cylinder Retract Speed
(60 x Retract Volume) ÷ (231 x GPM) = Retract Speed
Retract Speed = sec.
**faster than 8.9 seconds = good
0.38 CID/rpm
hydraulic gear
pump 3/4" keyed
shaft CW
$142
0.5 CID/rpm
hydraulic gear
pump 3/4" keyed
shaft CW
$146
0.61 CID/rpm
hydraulic gear
pump 3/4" keyed
shaft CW
$150
Which pump is our best choice?
Extend Speed = 15.18 sec.
Retract Speed = 11.39 sec.
Extend Speed = 11.54 sec.
Retract Speed = 8.65 sec.
Extend Speed = 9.46 sec.
Retract Speed = 7.10 sec.
gonna be so fast.
We'll beat Frank
for sure!
of ourselves.
be faster. But speed
alone is not enough to
beat Frank.
is?
might be enough to
power our pump. It's
certainly powerful
enough if we're just
pushing our cylinder
through open air.
not all we need it to do.
drive through logs!
displacement pump, which keeps putting
out flow...
hard work of splitting
a log.
no good if our engine's
not powerful enough to
keep it running.
enough power to meet the
system's pressure demands,
it might just give up and
quit in the middle of the race!
we have to be confident that
our engine will continue powering
our pump through even the
toughest logs.
if it's powerful
enough?
the stuff we already know
about our pump, engine, and
system. Plus a few handy
formulas.
Power Calculations
Things We Know:
System Stats (from FPA Triangle Calculations): 2000 psi max pressure
Displacement Pump Stats: 0.5 inch3(CID) displacement pump
Billy's Engine Stats: 10hp at 2000 rpm (highest engine speed)
Calculations:
1. Flow Rate at Highest Engine Speed (gallons per minute)
(Engine Speed (rpm) x Displacement (inch3)) ÷ 231 = gpm
This is our flow rate when the engine is running at full speed.
2. Can this flow rate be mainatined when chopping logs (system pressure of 2000 psi)?
Check if we have enough hp to maintain the flow rate at this pressure
(Pressure (psi) x Flow (gpm)) ÷ 1714 = Horsepower (hp)
Required hp = hp
≤10hp = good
Will Billy's 10 hp engine work?