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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.