Understanding
Hydraulic Pumps
The pump is that component of the hydraulic
circuit that converts mechanical energy into hydraulic pressure, which in turn
produces force in the cylinder. The mechanical energy can be supplied by hand,
by an electric motor, or by air pressure. Used less often are gasoline driven
internal combustion engine pumps. Hydraulic pumps are classified under the
broad category of pumps known as positive displacement. Positive displacement
(PD) pumps can produce fluid pressure either by rotating meshing gears of by piston
action. Sometimes in the case of two-stage pumps, both gears and pistons are
utilized. PD pumps require a provision of over-pressure protection. The
discharge pressure of hydraulic pumps has been standardized at 10,000 psi
(pounds per square inch).
What are some of the
other parts that work with pumps?
Critical mating
components of any hydraulic pump, and hydraulic circuit for that matter, are
the reservoir and the control
valve. The reservoir, or oil storage tank, is generally an integral
part of the pump assembly. The volume of the reservoir is important. The
control valve is either part of the pump assembly or is separately contained
within the hydraulic circuit. Correctly matching the control valve type to the
job application can not be overstated. Control valve selection is covered in a
separate section. See the diagram entitled Typical Circuit for a Hydraulic
Cylinder Jack to get a diagrammatic view of these and other
components.
Should I use a hand
(manual) hydraulic pump?
The hand hydraulic pump uses the simple principle of a
handle providing leverage to an internal piston. The piston forces hydraulic
fluid through a conductor (a hose) into the cylinder port. This style pump is
available in numerous sizes and can be used in nearly all cylinder lifting,
pushing, and pulling applications. The mobility provided by the feature of no
external power is a plus. Because they can be comparatively slow and
necessarily labor intensive, their recommended use is limited to less frequent
service needs like occasional maintenance tasks. Hand pump fluid volume and
fluid delivery speed can also become limiting considerations. Pressurization
times for applications that involve a large volume cylinder, or multiple
cylinders, can become lengthy. Especially Cylinders over 25 tons capacity with
long strokes require as many as 250-450 hand strokes to operate!
When should I use an
electric pump?
The electric powered hydraulic pump, while obviously more
expensive, provides an additional level of versatility. Non-manual external
power input permits cylinder use in high-cycle, production type settings. The
feed is AC single or three-phase voltage and the commercially available rated output
power varies from 1/3 to several horsepower. Additional weight associated with
external powered pumps can become a factor when portability is important.
Because there are so many pump options, selection of an electric pump to match
the application must be done with careful consideration. Small pumps using less
than 15 amps are ideal for use with less than ideal power supplies in the field
but pumps are slow. More powerful pumps require over 15 amps and are for use
inside facilities with reliable higher amperage power supplies.
When should I use a
pump driven by air?
Pneumatic (air) driven pumps have the same advantages and
disadvantages as electric pumps but are particularly suitable where shop air is
readily available. Required input pressure ranges from 40 to 100 psi. Air pumps
are suitable for non-explosive and non-sparking job environments. They convert
relatively modest source pressures to very high hydraulic pressures.
When should I use a
gasoline pump?
The gasoline driven internal combustion (IC) engine
hydraulic pump is suitable in situations where a manual pump is not
satisfactory and no electrical or pneumatic power source is available. An
example might be a remote construction site. IC engines are available in 2
cycle and 4 cycle models.
How fast will the pump
raise the cylinder?
The flow rate is the amount of oil, the pump
delivers to the cylinder (... for hand pumps with one hand stroke, ... for
electric and air pumps per minute). The larger the flow rate, the faster the
cylinder will rise.
Pumps are divided into three hydraulic fluid
flow rate categories:
1.
Low, which ranges up
to 15 fluid ounces (27 cubic inches) per minute.
2.
Medium, or between low
and high at about ½ gallon (130 cubic inches) per minute.
3.
High, which ranges up
to two gallons (830 cubic inches) per minute.
Hydraulic fluid flow rates are stated at the
standardized output pressure of 10,000 psi. During the course of operation, the
flow rate is large at pump start-up and declines rapidly to rated flow as
standard output pressure is reached.
Some pumps are equipped with double speed:
With the cylinder unloaded, the pump delivers a high volume of oil for fast
cylinder speed. Once the load is engaged, the pump automatically switches to
the slower high pressure lifting stage.
How many hand strokes are required for a hand
pump to raise a cylinder? Hand strokes = Cylinder oil capacity / flow rate.
How fast will an electric or air powered pump
to raise a cylinder? Time in minutes = Cylinder oil capacity / flow rate.
How do I pick the
right pump to fit my job?
Based on the unique features presented above
for each pump type, initial hydraulic pump selection is carried out in a
step-wise fashion by answering the following questions:
1.
What type of power is
available to run my pump? Do I have electricity, air, gasoline, or none of
these external power sources available? If all are available, which one is
best?
2.
Is this a one-time or
infrequent job need, or will repeated cycles or an extended time period be
involved? In other words, do I need a pump rated for rugged production
conditions? One rated for heavy-duty service? Or one which only needs to
tolerate light of intermittent service.
3.
Once begun, how
quickly do I need to accomplish each lifting, pushing, or retracting operation?
This will determine the required hydraulic fluid flow rate: Low, Medium, or
High.
4.
How many cylinders
will I need for this job and what will be the size of each? In other words, how
much total hydraulic fluid volume will the pump be required to accommodate,
i.e. how big should my pump reservoir be? Pump manufacturers list volumes in
cubic inches. To put this into perspective, one gallon is equivalent to 231
cubic inches. Reservoir volume should at a minimum be 1.5 times the total
cylinder volume.
Once these basic questions have been
considered, but maybe not completely answered, a more refined purchase
selection must be undertaken by answering the following specific questions:
For hand operated pumps: Do I need single or two-speed operation?
Single-speed models are good when a small cylinder stroke is involved.
Two-speed models cost more but provide time and manual energy savings when
large volume cylinders are being used. They operate on the principle of moving
a large volume of fluid under no-load initially and then slowing to produce
high pressure to take-up the load. Simplex (Actuant Corporation) only
manufactures two-speed hand operated pumps
For hand operated pumps: Do I need single acting or double acting
operation? This depends on whether your application employs a single acting or
double acting cylinder. Double acting hand hydraulic pumps have a special
directional valve that allows power strokes in two directions.
For electric powered pumps: Is portability a consideration or will my
job allow the pump to be permanently installed in a stationary location? Do I
have single phase or three phase voltage available? Just like hand operated
pumps, do I need a single or two-speed operation (see above).
For air driven pumps: Do I have a reliable compressed air source?
What is the maximum supply pressure? Will my compressed air source provide
enough air volume (cfm) to drive the air motor?
What additional
information do I need to pick a hand pump?
Reservoir volume must be matched to the size
and number of cylinders you are using.
Why are two volumes
sometimes listed for the same pump reservoir?
The physical size of the reservoir, the total
volume, is usually larger than that reservoir’s actual useable volume. If two
volumes are listed, always use the smaller value when selecting a pump
reservoir to match your total cylinder volume. Remember, reservoir volume
should at a minimum be 1.5 times the total cylinder volume.
What additional
information do I need to pick an air pump?
Air pumps rely on
specific amounts (flow volume) of driving air at a minimum pressure.
Consequently your source, usually an air compressor, must at least be capable
of producing both the minimum volume, often referred to as consumption, and pressure. Volumetric flow rates are
stated in standard cubic feet per minute, abbreviated SCFM.
How to match pump with
jack
1.
For low duty
applications, you need a pump that has 20% more usable oil capacity than the
total oil capacity in your jack(s). For low duty applications, you need a pump
that has twice the usable oil capacity than the total oil capacity in your
jack(s). Attention! The tank size is not equal the usable oil capacity. Make
sure to use "usable oil capacity" in your selection.
2.
The pump must match
the jack’s maximum operating pressure. Most US jacks and pumps operate at
10,000 psi under full load. All our cylinder jacks and pumps listed on our
website operate at the standard US pressure setting.
3.
Applicable for
electric pumps: A pump will push the oil through the hose at a certain speed
called the "flow rate". This will extend the jack either slowly or
fast. Depending on your application choose a pump with the desired speed.
4.
Applicable for
electric pumps: Pump models are available with different size motors (as
specified in horsepower (hp)). A smaller motor will have to work harder than
the larger motor. So if you are putting the pump under constant heavy duty
strain, choose a more powerful motor.