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    Hydraulic Cylinders



    Hydraulic Cylinders
    Hydraulic Seals
    and Guides
    c I H c I H

    C I H


    Fig.1: Double Acting Cylinder

    Fluid power systems transfer and utilise mechanical power through a working fluid. Energy is transmitted, stored and used through the transfer and pressure of fluids. By utilising differential surface areas acted upon by the pressure of the working fluid, a mechanical advantage can be achieved. There are two main types of fluid power systems:

    • Hydraulic: using liquid such as oil for the working fluid
    • Pneumatic: using gas such as air for the working fluid

    Hydraulic Cylinders

    Fig.2: Cylinder Types

    A hydraulic cylinder is a linear actuator used to push or pull a load, or to selectively resist motion under load by means of fluid pressure. Double-acting cylinders, the most common type, are able to push and pull (see Fig.1). High pressure fluid is pumped into the extend chamber port (Fig.1: A) and acts on the piston to push the piston rod out, thereby extending the length of the cylinder. Inversely, to retract the piston rod and reduce the length of the assembly, high pressure fluid is pumped into the retract chamber port (Fig.1: B) and acts on the opposite side of the piston.

    A cylinder which can only push but not pull is referred to as a single-acting cylinder. High pressure fluid is pumped into the extend chamber (Fig.2: A) and acts on the piston to push the piston rod out. An external force is required to return the cylinder to the retracted position. A typical single-acting cylinder can be found on a forklift truck where the load of the fork assembly (tines and carriage) enacted by gravity pushes the cylinder back into the retracted position. Multi-stage cylinders (also referred to as telescopic cylinders) have two or more piston rods in a coaxial arrangement to achieve a greater extended length compared to the retracted length.

    Cylinder Classification

    The type of cylinder and the application in which it’s used are two of the main criteria to determine which seals and guides are selected. Applications are referred to as light duty, medium duty and heavy duty. These classifications are somewhat subjective but the duty levels are typically characterised by the following criteria.

    Light Duty Cylinders

    Light duty cylinders are typically cylinders used for stationary equipment, indoors in a factory environment and may be characterised by:

    • System pressures up to 160 bar (2300psi)
    • Temperature up to 70°C (160°F)
    • Rare instances of pressure spikes in excess of system pressure
    • Minimal side loads acting on guides
    • Environment with moderate temperature fluctuations and relatively free of contaminates

    Medium Duty Cylinders

    Medium duty cylinders are typically used in agriculture, off-highway equipment and may be characterised by:

    • System pressures up to 250bar (3625psi)
    • Temperature up to 90°C (195°F)
    • Moderate pressure spikes in excess of system pressure
    • Environment with moderate temperature fluctuations with climate and typical external contaminates such as dust and moisture

    Heavy Duty Cylinders

    Heavy duty cylinders are typically used in off-highway earthmoving, mining and forestry equipment and may be characterised by:

    • System pressures of 400bar (5800psi) or more
    • Temperatures exceeding 90°C (195°F)
    • Regular pressure spikes in excess of system pressure
    • Heavy side loads acting on guides, usually due to heavy components and-or high accelerations.
    • Tough environments with wide ranging temperature fluctuations and typically harsh external contaminants

    Hydraulic Seals and Guides

    Fig.3: Heavy-Duty-Cylinder

    Hydraulic cylinder seals are used to seal the opening (clearance gap) between various components in the hydraulic cylinder. Fig.3 shows an example of the seal and guide components of a heavy duty cylinder.

    There are two main types of hydraulic seals in the system:

    • Dynamic seals seal between components in relative motion. In a hydraulic cylinder the rod sealing system seals dynamic reciprocating motion between the piston and rod head, while the piston sealing system seals dynamic reciprocating motion between the piston and cylinder bore
    • Static seals seal between components fixed together without relative motion. Hydraulic cylinders use static seal in various locations depending on the design and construction. The most common are the static seals between the piston and piston rod, and between the head and cylinder bore tube

    Figure 1

    Hydraulic cylinders are used to convert hydraulic power into linear motion. The amount of force a hydraulic cylinder can exert is a function of the piston area and the hydraulic pressure. This is represented by the formula:

    Hydraulic Cylinder Basic CircuitF = P x A where
    F = force in Newtons (N)
    P = pressure in Pascals (Pa)
    A = area in square meters (m2)
    A basic circuit to drive a hydraulic cylinder is shown in figure 1.

    When a double acting hydraulic cylinder is extending the oil pressure acts on the total piston area, however when the cylinder is retracting the area available is the piston less the rod. Therefore for the same pressure the hydraulic cylinder extending force will always be greater than the retracting force.

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    Jutta Tillery
    Jutta Tillery
    14:34 02 Apr 22
    Excellent customer service, kept us updated throughout the delivery process really looking forward to doing business with Waltan Tools again soon
    Daniel and Scott
    Daniel and Scott
    12:02 29 Jun 21
    We have done business with Winnellie Hydraulics on numerous occasions and find them to always be nothing but professional, honest and reliable.Their customer service is excellent and they are always a pleasure to work with. We would highly recommend Winnellie Hydraulics and we look forward to continuing business with Max and the team in the up and coming future.
    Damien Pedersen
    Damien Pedersen
    06:23 15 Feb 21
    Winnellie Hydraulics are up most professional and I am always impressed with the service offered and provided. The team at Winnellie Hydraulics are highly skilled, innovative and ever reliable. They continue to be the Territory’s leading service specialists within the fields of the hydraulic and pneumatic services and solutions. The team have a broad range of knowledge in hydraulic, pneumatic, hose management and products across a extensive range of divisions. The team at Winnellie Hydraulics are easy to work with and really appreciate their customers and strive for continuous business improvement.
    Rob North
    Rob North
    07:53 10 Feb 21
    Efficient, professional and dedicated. The team at Winnellie Hydraulics are a pleasure to work with and are customer service specialists.Max and the team have taken on many challenges to assist with emergent scopes at our onshore facility in Darwin. They go above and beyond to meet the timeline required without missing a beat on quality.I highly recommend dealing with them and look forward to future business.Thanks guys
    Sonia Harvey
    Sonia Harvey
    05:25 08 Feb 21
    The team at Winnellie Hydraulics are customer service specialists! They certainly go above and beyond to meet the needs of customers and are a great local service and supply business. I highly recommend dealing with them.
    Darren Steele
    Darren Steele
    02:59 07 Feb 21
    For all your Hydraulic & Pneumatic needs, Winnellie Hydraulics has you covered.Max and the team run a great operation that supports the Oil & Gas and Mining industries.With great brands supporting them, they are truly the one stop shop for all your engineering needs.
    Dipak Nand
    Dipak Nand
    23:06 04 Feb 21
    The team at Winnellie hydraulics, is great to work with, they understand our priority and service delivery to our Defence clients, No job too small or big and delivering of high quality products and service. Also really easy to deal with in regards to faults/ warranty and SME service . Highly recommended to use.
    Darren Upton
    Darren Upton
    22:54 04 Feb 21
    Winnellie Hydraulics are a Parker PPD for the NT which means they have full access to all Parkers Hannifin products & our local Engineering team in Australia who can work with Winnellie on any projects where clients needs are meet using Parkers products & their insulation experience
    Ben Tilbrook
    Ben Tilbrook
    07:35 04 Feb 21
    Outstanding commitment to their customers, in my experience there isn’t anything that is too hard for this mob. Always prepared to find solutions to their customers now matter how big or small the request. A great family business who take pride in providing product and service.
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