HYDRAULIC CYLINDERS FOR HEAVY DUTY EQUIPMENT AND MACHINES

NFPA CYLINDERS:

and CUSTOM HYDRAULIC CYLINDERS

CYLINDER SELECTION

A fluid power cylinder is a device consisting essentially of a movable piston and rod assembly contained within a cylindrical bore which is actuated by an operating medium and uses the pressure of that fluid to produce mechanical force and linear motion.

The power output, or thrust, produced is the product of the system pressure (psi) multiplied by the square inch area of the internal piston surface upon which that pressure acts.

The proper selection of a fluid power cylinder requires the consideration of numerous factors influenced by the expected application conditions.

Those factors include the cylinder mounting style, stroke length, cycle speed, operating pressure, operating media, mounting attitude, direction of work force, and means of stopping the work load after it is put in motion.

Prior to selecting a model for use, the engineering information section which follows should be thoroughly reviewed and the final cylinder specifications established as  a  result  of  determinations  based  on  design recommendations applicable to the intended use.

The given information will aid in the selection of the proper  cylinder  bore,  mounting,  rod  diameter,  and the inclusion of recommended optional construction features.

 

MOUNTING INFORMATION

Cylinders are manufactured in numerable combinations of bore, rod, and stroke sizes with various standard mounting styles.

There  is  a  direct  relationship  between  the  cylinder mounting style and the effects of the operating pressure upon the unit. The following information should be considered to assist in the selection of the proper style mounting for use in the intended application.

Standard mounting styles for fluid power cylinders are divided into two general classifications and three groups based upon the combined effects of force direction and mounting conditions. Those classifications are as follows:

Class I: Cylinders which produce a straight line transfer of force.

This class consists of models having fixed mounting styles that are secured in a rigid condition. Cylinder mountings of this type are divided into two groups: those models which absorb force on the cylinder centerline and those styles which do not absorb force on the centerline of the unit.

Class II: Pivoted cylinders which transfer force along a variable path.

This group consists of mounting styles which pivot around a fixed pin and are able to compensate for alignment changes in one plane during operation.

The way in which a cylinder is mounted is critical to its performance and service life. Improper mounting can result in damage to the cylinder as well as to the equipment on which it is being used. Inaccurate
installation, or the use of an inappropriate mounting style may result in misalignment which causes harmful side loading, bending, and the unsafe operation.

Cylinders Having Fixed Centerline Mounting

Mounting styles which allow the thrust produced by the cylinder to be absorbed in a plane coincident with the centerline of the unit are most desirable since the mounting bolts are subjected to straight line shear or tension loads only. Cylinders are not subject to forces which tend to sway or flex the unit as occurs with certain alternate style mountings.

Flange Type Mountings

Proper selection of a flange mounting style depends upon whether the primary work direction results in tension or compression loads being carried by the cylinder rod.

Front flange mounted units are preferred for “pull type” applications where the rod is held in tension. “Push type” applications which subject the cylinder rod to compression loads are best suited for rear flange style mountings.

Flange mount models are of the fixed centerline class, but if improperly mounted by the backside of the flange (mounted against flange face nearest the cylinder body) they may be subjected to destructive bending forces that can distort the mounting plate or fatigue the fasteners holding the assembly.

The only flange styles suitable for backside mounting are models which feature the end cap and flange combined as an integral component.

Rectangular flange mount styles may be subject to pressure  limitations  which  vary  with  bore  size,  rod diameter,  and  stroke  length.  These  conditions  are explained in greater detail in the text material pertaining to the various models available in these mounting styles.

In applications which involve operating pressure levels in excess of those permitted with rectangular flange

models, the square flange mounting styles should be considered. This style provides a stronger mounting flange  which  permits  operation  at  higher  working pressure and provides more stable support for long stroke cylinders.

This model provides the most rigid flange mounting available and is preferred for high pressure applications or those involving long stroke lengths.

Extended Tie Rod Mounting

Cylinders which use extended tie rods for mounting purposes are available with the tie rod extension on the rod end, blind end, or both ends as required to suit  application  conditions.  The  location  of  the  tie rod extension must be specified at the time of order placement.

The general use recommendations given for flange mount models also apply to units mounted by the tie rods. This mounting style provides a stable means of handling thrust loads and may be used whenever available clearances permit the installation of this model. Consideration  should  be  given  to  providing  added support to the cylinder body on horizontally mounted units having long stroke lengths.

Centerline Lug Mounting

Centerline  lug  mounting  is  the  most  stable  of  the fixed  mounting  styles  secured  with  mounting  bolts perpendicular to the unit centerline since it is the only model which has the mounting points located on a plane coincident with the cylinder centerline.

Holding bolts are subject to straight line shear or tension loads only rather than more complex forces which are developed in all other models which have the mounting bolts similarly positioned but at non-centerline locations. In applications involving high pressure or shock loads, the cylinder should be secured to the mounting surface by dowel pins placed through the mounting lugs. The lugs include sufficient clearance for the addition of such pins.

Dowel pins, which minimize deflection, should be placed at one end of the cylinder only regardless of stroke length, with the end to be pinned determined by the primary work force direction and application conditions.

Cylinders should be pinned on both sides of one end and never through only one lug. Pinning one corner, or two corners located diagonally across the unit can
result in severe warping and distortion of the cylinder assembly.

Fixed Non-Centerline Type Mountings

Cylinders with fixed non-centerline mounting styles are secured by fasteners located on a plane which is parallel to, but not coincident with the centerline of the unit.

Since the mounting bolts are not on a common plane with  the  cylinder  centerline,  they  are  subjected  to stresses which tend to flex the end caps about the mounting bolts resulting in a swaying type motion.

This motion in itself is not harmful to the cylinder, but does compound stress forces acting upon the mounting bolts. Due to the forces developed, high tensile cap screws are recommended for mounting all cylinders. To protect the cylinder mounting from the effects of high stress levels, the use of shear keys or dowel pins should be considered. These components absorb shear forces developed at the cylinder mounting surfaces and reduce the load carried by the mounting bolts.

Shear keys should be placed at the proper end of the cylinder as determined by the primary work force direction. They should be located behind the front or rear head of the cylinder when the work direction places the rod in compression, and on the front side of the front head when the rod is in tension.

An extended key retainer plate is available and should be considered for use when a keyway can be milled into the surface on which the cylinder will be mounted. This optional feature absorbs shear loads and promotes accurate alignment during installation of the unit.

Dowel pins can also be used to absorb shear forces and assist in maintaining proper alignment. The mounting lugs of foot mount cylinders have sufficient length for the addition of these locating pins. Pins should be placed through both lugs at either end of the unit as determined by application conditions.

Cylinders should never be pinned through one lug only, diagonally across corners, or through all four lugs at
both ends of the unit. Improper pinning may result in severe warping, distortion, and possible damage to the unit.

Pivoted Centerline Mounts

When the application requires the cylinder rod to travel a curvilinear path, a unit with a pivoted type mounting is necessary.

The application conditions dictate which style mounting is best suited for use. Consideration should be given to the path of travel and possible locations for the placement of fixtures necessary to mount the various model units.

When  using  cylinders  with  pivoted  mountings,  it  is necessary to include a rod end attachment which will

allow rotation in one plane.

Front trunnion and intermediate trunnion models having the trunnion pins located close to the front head can use smaller diameter rods without danger of buckling than can other models which have the mounting located toward the rear end of the unit.

Front pivoted models are also less likely to require stop tubing than cylinders which pivot from the rear. Refer to the stop tube information located within the engineering section for an explanation of this requirement.

Trunnion Mount Models

Trunnion mounted cylinders require rigidly anchored, accurately  aligned  pillow  blocks  mounted  over  the trunnion pins placed as close to the cylinder end cap as clearances will permit. Bearing support should be provided for the full length of the pins. Trunnion pins are intended to carry shear loads only and should not be subjected to bending loads.

Self aligning bushings should never be used to support the trunnion pins since they will allow bending forces to act on the cylinder mounting.

Intermediate trunnion models can have the trunnion
centerline located at any point between the cylinder end caps. The desired trunnion position (designated as the “XI” dimension) should be specified at the time of order placement. While the trunnion centerline can be specified at virtually any position, its location cannot be altered significantly after construction is complete.

Clevis And Pivot Mount Models

Clevis and pivot mounted cylinders are pivoted around a fixed pin located at the rear end of the unit.

A clevis pin of sufficient diameter to withstand the shear loads generated by the cylinder when operated at the maximum rated pressure is available for use with these models.

The spherical bushing mount is the only mounting style designed to allow for misalignment.

When selecting an accessory to satisfy the requirement for a pivoted rod end connection, a component with a pin diameter equal in size to the mounting base pin should be chosen if possible.

Thread modifications, either to the rod end or accessory, are  alternate  construction  options  that  should  be considered for use to obtain equal pin diameters at both ends of the cylinder.

STANDARD CYLINDER SEALS

Standard cylinders include seals of Polyurethane and Teflon with the seal compound and location of use dependent on the design purpose of each model.

Seals of internally lubricated Polyurethane are commonly used as rod and piston seals, with the material selected for use based on its performance characteristics and the application requirements.

Teflon is used to seal the Cushion Adjusting Screw and Ball Check assemblies and for Piston Seals and Back Up Washers for certain seals in units suitable for high pressure service.

The  seal  material  specifications  for  any  particular cylinder can be determined by referring to the “Design Feature” information given for available models.

Polyurethane may be used from 65oF to +200oF. Teflon is unaffected by extreme temperatures and is not a factor in limiting service conditions.

Cylinder operation is not suggested near either end of the seal temperature range. Standard models are recommended for use at temperatures from -20oF to +180oF (-29oC to +83oC). When the operating fluid contains water, the maximum operating temperature should not exceed +150oF due to adverse effects of hot water on seals of Polyurethane.

Viton* Seals

Cylinders  may  be  equipped  with  seals  of  Viton (fluorocarbon  rubber)  to  suit  elevated  temperature or fluid compatibility requirements when application conditions preclude use of standard materials. Viton is recommended for use with:

• Pneumatic service

• Petroleum oils and fluids

• Selected phosphate ester fluids

• Halogenated hydrocarbons

• Silicone fluids

Viton is suitable for use at temperatures from  -20o F to +400o F (-29o C to +204o C). This material will withstand intermittent use to +550o F, but is subject to substantial seal life reduction with prolonged exposure to temperatures above +400o F.

770-316-4951

Carboxylated Nitrile Seals

Carboxylated Nitrile (CN) Seals are available for use in high speed/high cycle applications for air or hydraulic service. They are also suitable for use with water or water based fluids. CN Seals are recommended for:

• Pneumatic service

• High speed/high cycle applications

• Water/water based fluids to 210o F

• HWBF (high water base fluids)

Alternate  seal  materials  are  available  upon  request for use with other types of operating fluid or higher temperature requirements.

Seal Design Modifications

Rod  and  piston  seals  are  available  in  a  variety  of design configurations. While standard GHC cylinders include  seals  proven  to  be  satisfactory  for  general purpose  use,  alternate  styles  designed  to  provide specific performance characteristics are available when application requirements make their use desirable. Seals that offer extended service life, greater sealing efficiency,
lower friction, constructed of materials, or in sizes better suited to meet particular design requirements may be specified. A glass fiber filled teflon sealing ring installed over an elastomer expander provides a long wearing, bidirectional, low bypass piston seal suitable for air or hydraulic service.

Wear rings of similar material are often used with this type of seal. Their use eliminates metal to metal contact between  piston  and  bore  surfaces  which  improves wear conditions and is especially effective when used in models having long stroke length. Seal construction options are an extra cost feature available upon request in all cylinders. Consult GA Hydraulic Cylinders, Inc.
to obtain design recommendations and price adders when this optional feature is being considered.

CYLINDER CUSHION INFORMATION

Internal cushions at the end of the cylinder stroke are optional and can be supplied at either one or both ends of the unit as desired. The use of a cushion is recommended for high speed, high impact applications to reduce noise, vibration, and the destructive hammering
effect of the piston assembly bottoming against the cylinder end cap. The use of cushions does not affect

cylinder envelope or mounting dimensions. The cushion functions by closing off the inner exhaust
orifice,  trapping  the  operating  media (either  air  or hydraulic fluid), and developing a backpressure against the advancing piston which slows, or cushions, the travel speed.

As the piston approaches the cushioned end of the cylinder, the exhaust flow is closed off by a bushing or plunger which enters the close fitting cushion cavity of the end cap.

A cushion adjusting screw are provided in the end cap of all cushioned models with the exception of the rod end head of 11/2 , 2, and 2¹/2 bore cylinders equipped

with the largest available oversize piston rod. These size combinations are provided with a nonadjustable cushion due to insufficient clearance in the head for adjustment screw.

The rate of effective cushioning can be regulated by use of the cushion adjusting screw. When the mating cushion surfaces engage, and the operating media being exhausted is trapped by the advancing piston, the exhaust flow opens cushion valve and exhausts fluid through an orifice.

The degree of cushion effect can be regulated by metering the flow of trapped operating media through the orifice. Turning the adjusting screw affects the rate at which the trapped pressure is relieved and permits control of the cushion to the desired level.

The function of the ball check valve is to assist in disengaging the cushion when the stroke direction is to be reversed.

Without the ball check valve, fluid pressure applied through the cylinder port can act only upon the cross sectional area of the cushion itself. The ball check orifice permits incoming flow from the port to go directly to the full face of the piston, thus greatly increasing the cylinder thrust capability and reduces the time necessary to break away from the engaged cushion.

Cushion  adjusting  screws  are  interchangeable  with each other and do not protrude beyond the edge of the cylinder head.

The cushion adjusting screw is normally located on side #2 unless the mounting style or port position does not permit. This component can be identified by the socket head of the screw. The cushion effect can be controlled by turning the inner screw with a standard hex key wrench. Turning this screw in a clockwise direction will increase the cushion effect, while turning it in a counterclockwise direction will decrease the cushion effect.

Cylinders  having  the  cushion  adjusting  screw  at  a position  other  than  on  side #2  may  be  ordered  if desired. Include this information with order and specify the position by using the reference number assigned to the side location required.

FPA Cylinder Accessories

NFPA Cylinder Accessories

Georgia Hydraulics offers a complete lines of hydraulic cylinder mounting accessories to assure flexibility and versatility in present or future cylinder applications, and our products are applicable to various NFPA mounting style(ME,MF,MP,MX,MS,MT) and serve many manufacturer & distributor across North America in  OEM&MRO markets.

  

Our 260,000 square foot manufacturing plant is located in Austell, Georgia.  We are ISO 9001 and ISO 14001 certified.

Our original and brand replacement cylinder components lines as follows:

   

Ø  Rod Clevis

Ø  Rod Eye

Ø  Rod Dual Eye

Ø  Clevis Bracket

Ø  Eye Bracket

Ø  Spherical Rod Eye

Ø  Spherical Eye Bracket

Ø  Detachable Mount

Ø  Flange Coupler

Ø  Weld Plate

Ø  Alignment Coupler

Ø  Pivot Pin

Ø  Piston

Ø  Fitting/Adapter

What you will need to know before buying a new cylinder:

Considered:

•  Bore Diameter: It is the diameter of the cylinder bore. We offer bores from 1.5 inches wide to 20 plus inches wide.

•  Maximum operating pressure: The maximum working pressure a cylinder can carry is known as maximum operating pressure. We offer low pressure cylinders up to 3000 psi.

•  Rod Diameter: It is the diameter of the piston or the rod that are used in hydraulic cylinders.

•  Stroke: The distance traveled by a piston in a hydraulic cylinder is known as stroke. The length of a stroke could be several feet, or a fraction of an inch.

•  Types Of Cylinders that we offer at Georgia Hydraulics International: tie-rod cylinders, ram cylinders, mill style cylinders, and welded cylinders.

www.vphyd.com

770-316-4951

email: rstom03@aol.com