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Hydraulic Cylinders Instruction And Manual About How Release The Air From It (Hydraulic Cylinder Repair)

At first guide to hydraulic cylinder-Hydraulic Cylinder Repair

  • The hydraulic cylinder first appeared at the end of the 18th century. The hydraulic system is based on Pascal’s fluid pressure law, which states that when pressure is applied to the fluid, equal pressure will be applied in all directions of the whole fluid.
  • Hydraulic cylinders can be used in any application requiring strong thrust or tension. They first discovered many uses during the industrial revolution, when the increase in factories and production required a variety of hydraulic applications. Now, hydraulic cylinders are widely used in various industries, including construction, manufacturing, mining and offshore industries.


Single acting hydraulic cylinder-Hydraulic Cylinder Repair

The single acting cylinder works when thrust or tension is required, so the hydraulic oil acts only on one side of the piston rod. Another force, such as gravity, the weight of a load, or a spring, operates the cylinder in the other direction.

Double acting hydraulic cylinder-Hydraulic Cylinder Repair

The double acting hydraulic cylinder forces the piston rod to move forward and backward through hydraulic operation.

Telescopic cylinder-Hydraulic Cylinder Repair
  • Telescopic cylinders use the cylinders in the cylinders to increase the distance that can be raised in one stroke. Stroke refers to the amount that the oil cylinder can lift in one movement. It is usually used for machines such as tippers, They can also be used for any additional stroke required (the amount of movement produced by the cylinder) without increasing the space required for the envelope.
  • The telescopic cylinder can be double acting or single acting. A potential problem is that the standard telescopic cylinder will have a sudden change in speed due to the change of volume in different cylinder stages. However, professional engineering can produce double acting telescopic cylinder, which can Move at a constant speed.
Socket cylinder-Hydraulic Cylinder Repair

The jack cylinder is a mobile cylinder with a series of dimensions. Generally, a manual pump can use multiple sizes of cylinders, which means that the company can choose the best cylinder size for each job. Jack cylinders have no supports and are usually used only on the ground. Typical lifting weights are 5 tons, 10 tons, 20 tons and 50 tons. The standard size and moving nature of Jack cylinders make them ideal tools that are not often needed. In many cases, instead of owning a hydraulic cylinder, the company leases a jack cylinder when a specific job requires it.


  • Pascal’s law shows that.
  • Force = pressure x area
  • In a hydraulic system, the pressure is given by the HPU (hydraulic pump unit). The area refers to the size of the hydraulic piston. These two parts determine the force that can be applied by the cylinder.
    Therefore, the weight that the hydraulic cylinder can push or lift is equal to the pressure provided by the pump multiplied by the size of the cylinder rod.
  • Most pumps have a standard range; Typically from 3000 psi to 10000 psi (210 to 690 bar). The average is often at the low end of the range; about 210 bar. A pump can lift an infinite weight, depending on the size of the cylinder. Increasing psi may require adjusting the seal, valve and cylinder design to cope with the increased pressure.
    The pump also determines the operating speed of the cylinder because it provides hydraulic oil at the necessary flow rate.

HOW TO SIZE A CYLINDER-Hydraulic Cylinder Repair

  • The Hydraulic Cylinder Repair designer needs to consider the size and size of the hydraulic cylinder. If an oil cylinder reaches out too long, there is a risk of buckling – which means that the work quantity of rod and barrel must be increased. However, this increase in area will produce greater force, which may lead to excessive manufacturing engineering and make it heavier.
  • Create a Hydraulic Cylinder Repair at the apex
  • Design
  • The cylinder is first designed by a team of Hydraulic Cylinder Repair engineers, considering the purpose of the hydraulic cylinder and its environment. This determines the materials, coatings, seals and other professional components. The design of the hydraulic system shall comply with any external legislation related to the industry in which it is designed. In particular, there are many requirements in the offshore industry, and apex hydraulic can design according to these requirements.
  • Machining plant
  • Once the design is completed, the engineers in the machinery workshop begin to produce the oil cylinder. Cylinder rods and other components are drilled with highly specialized machines to achieve accurate measurements. The cylinder rod is chrome plated or coated with a professional coating such as COREX.

FITTING DEPARTMENT-Hydraulic Cylinder Repair

The fitting department puts all the components together (rod, pistons, tubes and seals). Purchasing from a wide variety of high-quality manufacturers, Apex Hydraulics are not tied to any one product and are able to choose the most appropriate part for each cylinder. The fitting department assembles the cylinder, ready for inspection and testing.

The in-house inspection department offers rigorous testing of all hydraulic cylinders before they are approved for the client. They perform pressure, pull and load tests as required. Apex are able to facilitate all third-party inspection agencies that may be required for offshore work, including DNV-GL, ABS and Lloyds Register.

Parts are spray painted in house. They can be painted to any required standards. Paint standards for offshore hydraulic cylinders are particularly specialised, with Norsok providing a range of that is typically approved by inspection agencies. At the point of painting, company logos or details can be added.

  • HYDRAULIC CYLINDER PARTS-Hydraulic Cylinder Repair
  • CYLINDER TUBE / CYLINDER BARREL-Hydraulic Cylinder Repair
  • The cylinder tube (or barrel) is made of steel; usually carbon steel. There are a range of different steels available in terms of strength, with higher pressures requiring stronger steels and thicker cylinder walls. In places where it cannot be painted (such as food preparation areas) it would be made of stainless steel to avoid it being prone to corrosion. The cylinder barrel can be coated in a variety of paint or coatings, with company logos often displayed here.
  • The internal diameter of the tube usually needs no protection with paint or chrome because the hydraulic fluid protects it from corrosion. However, if the hydraulic fluid is a corrosive material (such as water) the inside of the tube will be coated as well as the rod.
  • The cylinder rod is the only external part that can’t be painted. Because of this, it has to be protected in other ways. In order for the cylinder to work well the coating has to be completely smooth. The cylinder rod needs to be highly resistant to pitting, corrosion or wear. Any cracks can scrape on seals, causing contamination to enter the hydraulic fluid and leading to eventual hydraulic system breakdown. Therefore, the materials and coating of the hydraulic cylinder is of the utmost importance.
  • Most commonly, the cylinder rod is made of steel or stainless steel and is then coated with Hard Chrome Plating (HCP). However, a number of even more hard-wearing coatings have been developed, including COREX – a specialised coating developed by Apex Hydraulics which can be up to ten times less porous than HCP, with hardness of up to 1400Hv; double that of HCP. Extreme environments may require different materials, such as Inconel, which is particularly corrosion resistant.
  • The piston is attached to the piston rod and moves up and down the cylinder bore, pushed by the hydraulic fluid. It provides the area used to create the hydraulic force. It is vital that no hydraulic fluid can pass over the internal piston.
  • HYDRAULIC FLUID-Hydraulic Cylinder Repair
  • Most hydraulic fluids are oils, with a huge number of different types available. Different hydraulic systems, pumps and valves will require a different viscosity of fluid. Sometimes, in applications where any flammable liquid poses a risk, the hydraulic fluid may be water based.
  • Both ends of the hydraulic cylinder need a mounting interface; one at the base and one at the head. The mounting interface depends entirely on the customer requirements and application of the fabrication.
  • Different mountings include: Pins; Threaded connections; Flanges; Trunnions; Spherical bearings; Foot mounted; Bolted
  • The hydraulic tube needs to be sealed at both ends to stop oil leaking and keep the pressure in. One end of the tube is sealed off with a base. However, the other end needs to be open to allow the rod to move in and out of the tube. At this end the tube is sealed with a neck gland that allows the rod to move in and out. The neck gland material would be chosen during design, with seals on both the rod and the tube.
  • Hydraulic fluid needs to enter and exit the cylinder via ports, with one port at either end of the cylinder tube and the hydraulic piston between the two ports. These must be secure, as a weak port can cause a dangerous leak of hydraulic fluid under intense pressure.
  • Seals are used throughout the hydraulic cylinder. They can be made of a wide variety of different materials, depending on the function and type of hydraulic cylinder. They need to be hard wearing, able to survive multiple repetitions of the rod moving in and out of the barrel, removing any contamination.
  • Hydraulic cylinder designers will select the right seal for the cylinder application, taking multiple factors into account. Cylinders that operate at very high temperatures will require seals that are not prone to melting, and so they may select a material such as Viton. At the other end of the spectrum, cylinders working at freezing temperatures will need a polyurethane material that won’t crack in the severe cold.
  • Zurcon and PTFE seals may be chosen for circumstances where seals are required to withstand the friction associated with very quick repetitions, such as in a factory environment.
  • Specialist seals can also be designed with back up rings (for seals working under intense pressure) and seals with an extremely tight closure (for very thin hydraulic fluid that can leak out of standard seals).
  • Valves and pumps are connected to the hydraulic cylinder via feed pipes and hoses. These are highly specialised, having to work under extreme pressures. They also need to be able to resist corrosion, so will be made of a material suitable for the outside environment as well as the relevant hydraulic fluid.
  • FILTRATION-Hydraulic Cylinder Repair
  • Filtration is vital to the hydraulic system. Hydraulic fluid must be kept entirely free of contaminants in order to ensure that seals are not damaged, and the system remains working well. There are a number of filters throughout the hydraulic system and depending on the environment of the machinery, these will need to be regularly changed. Some highly contaminated locations, such as factories, may benefit from bypass filtration units, which allow the filters to be changed without stopping the machinery. The filtration system can be isolated from the rest of the hydraulic system – the filters can be changed quickly and easily and then the system reattached. This has been found to increase the lifespan of the hydraulic system without the need for expensive services.
  • How to Properly Bleed Air from a Dump Truck Cylinder -Hydraulic Cylinder Repair
  • Trapped air can contaminate the hydraulic fluid in your system and affect overall performance. For this reason, bleeding air from dump truck hydraulic cylinders should be part of your regular maintenance program and performed before installing a new hydraulic cylinder.
  • Bleeding dump truck hydraulic cylinders involves bringing air to the top of the cylinder, then releasing the trapped air. The process varies slightly depending on the type of cylinder installed and whether you have a bleeder valve on your dump truck cylinder below.
  • Follow the steps for your cylinder type below to bleed air from a dump truck hydraulic cylinder properly.

Bleeding Air From Single-Acting or Lift Dump Truck Hydraulic Cylinder Repair


Raise the dump body and cylinder to full extension. Let the dump truck body stay in this position for a few minutes and let the air rise to the top of the cylinder.

  • Lower the dump truck cylinder until the front end of the dump truck body is about 2 feet from the chassis frame.
    Place the body lifting lever in the middle / fixed position.
    If your dump truck hydraulic cylinder has an external bleeder valve, open the valve. If the bleeder valve is located on the top of the cylinder, remove the tank cap with a wrench, move it to the inside of the vehicle body, and then open the bleeder valve.
  • Wait until all trapped air is discharged from the valve and a whole stream of hydraulic oil flows out of the valve.
  • At this time, the cylinder has been deflated and the vent valve can be closed.
  • Bleed the air from the rod cylinder-Hydraulic Cylinder Repair
    Before releasing the air in the dump truck cylinder, ensure that the hydraulic cylinder is not pressurized under any circumstances. When the hydraulic cylinder is in the horizontal position, the bleeder valve should point upward. The piston rod must initially be in the fully retracted position.
  • Open the air valve at the upper side of the hydraulic cylinder.
  • Check all hoses or pipes the sure they are connected properly.
  • Set up the hydraulic system and start it up.
  • Extend the piston rod slowly with no pressure built up. Keep extending the piston rod until there is oil/foam coming out of the air valve. (Hydraulic cylinders that go over-center must be air-released before mounting in the construction!)
  • Shut down the system and close the air valve.
  • Depressurize the system before opening the air valve at the lower side of the hydraulic cylinder.
  • Startup the hydraulic system.
  • Retract the hydraulic cylinder slowly with no pressure built up. Keep retracting the dump truck cylinder until there is oil or foam coming out of the air valve.
  • Shut down the system and close the air valve.
  • Retest the hydraulic cylinder by extending and retracting the piston rod until it is running smoothly.
  • Refilling Your System with New Hydraulic Fluid
  • Refilling your system with new fluid after bleeding air from your dump truck cylinders will further improve performance.  Always use clean, high-quality fluid with the right viscosity to ensure your cylinders operate smoothly and efficiently.
  • Help prevent hydraulic system contamination by only using fluid that has been stored properly. Other fluid contamination prevention measures include installing fluid bypass filters and replacing worn valves and components during preventative maintenance.
  • At Hydraulic Cylinders Inc, we have the product & knowledge to serve you in choosing the right dump truck cylinder for your equipment. Contact us to discuss your hydraulic cylinder needs or explore our blog to find answers to common hydraulic cylinder maintenance questions.
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