A Hydraulic cylinder (also known as linear hydraulic motor) is a mechanical actuator used to give a unidirectional force through a unidirectional stroke. It has many applications, notably in construction equipment and engineering vehicles, manufacturing machinery and civil engineering.
Hidromec thanks to the expertise of his staff is able to invent, design, build, maintain and improve cylinders for your individual applications.
Engineering is a technique of execution and control of compliance: a difficult result to achieve. A proven and certificated ISO9001model which splits into several phases: it starts from the verification and control of the materials of each single component to the analysis of the surface treatments (coatings) up to Reverse Engineering of subcomponents made in order to reach a products and subcomponents quality standard and create a conformity database.
Non elastic buckling
loads (Tetmajer’s calculation) andn
In hydraulic cylinder Euler’s calculation is basically the calculation used, as the piston rod may usually be considered to be a slender strut (negligible diameter).
Buckling load and operation load are then calculated as follows:
Buckling load K= ………In
The length to be used as the free buckling length may be determined from the Euler loading cases (see table 4). In order to simplify the calculation the stiffening due to the cylinder tube is ignored. This provides the required safety margin in standard cylinders, the installation position of which is usually not known, in order to cater for any superimposed bending loads..
Table 4: Euler’s loading cases
Hydraulic force - area formulas and calculator
The force produced by a double acting hydraulic piston on the rod side can be expressed as
F1 = (π (d22 - d12) / 4) P1 (1)
F1 = rod pull force (lb, N)
d1 = rod diameter (in, m)
d2 = piston diameter (in, m)
P1 = pressure in the cylinder (rod side) (lff/in2 (psi), N/m2 (Pa))
The force produced opposite the rod can be expressed as
F2 = (π d22 / 4) P2 (2)
F2 = rod push force (lb, N)
P2 = pressure in the cylinder (opposite rod) (lff/in2 (psi), N/m2 (Pa))
Rod pushing force for hydraulic cylinders are indicated below:
- 1 psi (lb/in2) = 144 psf (lbf/ft2) = 6,894.8 Pa (N/m2) = 6.895x10-3 N/mm2 = 6.895x10-2 bar
- 1 N/m2 = 1 Pa = 1.4504x10-4 lb/in2 = 1x10-5 bar = 4.03x10-3 in water = 0.336x10-3 ft water = 0.1024 mm water = 0.295x10-3 in mercury = 7.55x10-3 mm mercury = 0.1024 kg/m2 = 0.993x10-5 atm
- 1 lbf (Pound force) = 4.44822 N = 0.4536 kp
- 1 N (Newton) = 0.1020 kp = 7.233 pdl = 7.233/32.174 lbf = 0.2248 lbf = 1 (kg m)/s2 = 105 dyne = 1/9.80665 kgf
- 1 in (inch) = 25.4 mm
- 1 m (meter) = 39.37 in = 100 cm = 1000 mm
Rod pulling force for hydraulic cylinders are indicated below:
The selection of a piston rod for thrust (push) conditions requires the following steps to be carried out:
1. Determine the type of
cylinder mounting style and rod end connection to be used. Consult the Stroke
Factor table and determine which factor corresponds to the application.
2. Using this stroke factor, determine basic length from the equation:
Basic Length = Net Stroke x Stroke Factor
( The Piston Rod Selection Chart, below, is prepared for standard rod extensions beyond the face of the gland retainer. For rod extensions greater than standard’ add the increase to the stroke to arrive at the basic length’)
3. Find the load imposed for the thrust application by multiplying the full bore area fo the cylinder by the system pressure, or by referring to the Push and Pull Force charts.
4. Using the Piston Rod Selection Chart below, look along the values of ‘ basic length ’ and ‘ thrust ‘ as found in 2. and 3. above, and note the point of intersection.
piston rod size is read from the diagonally curved line labeled ‘ Rod Diameter
‘ above the point of intersection.
Long Stroke and Stop Tubes
When considering the use of long stroke cylinders, the piston rod should be of sufficient diameter to provide the necessary column strength.
For tensile(pull)loads, the rod size is selected by specifying standard cylinders with standard rod diameters and using them at or below the rated pressure.
For long stroke cylinders under compressive loads, the use of stop tubes should be considered, to reduce bearing stress. Selection of a stop tube is described.
OF CYLINDER DIAMETER
Given that the load and operating pressure of the system are known, and that a piston rod size has been estimated taking account of whether the rod is in tension(pull) or compression (push), then the cylinder bore can be selected.
If the piston rod is in compression, use the ‘Push Force’ table below.
Identify the operating pressure closest to that required.
2. In the same column, identify the force required to move the load (always rounding up).
3. In the same row, lock along to the cylinder bore required.
If the cylinder envelope dimensions are too large for your application increase the operating pressure, if possible, and repeat the exercise.
If the piston rod is in tension, use the ‘Deduction for Pull Force’ table. The procedure is the same but, due to the reduced piston surface area resulting from the piston rod, the force available on the ‘pull’ stroke will be smaller, To determine the pull force.
Follow the procedure given for ‘push’ applications as described above.
2. Using the ‘Deduction for Pull Force’ table below, establish the force indicated according to the rod diameter and pressure selected.
3. Deduct this from the original ‘Push’ force. The resultant is the net force available to move the load.
If this force is not large enough, go through the process again but increase the system operating pressure or cylinder diameter if possible. If in doubt, Our design engineers will be pleased to assist.