Types of Hydraulic and Pneumatic Seal
Other important parts that are worth mentioning, inside this system, in both Cylinder hydraulic and Cylinder pneumatic there is a seal kit placed inside the cylinder. As in other parts, the cylinder Seal Kit also consists of several smaller parts, these parts are Piston Seal, Rod Seal, Dust Seal or Wiper and O-ring, which is the link between the cylinder parts.
Seal hydraulic comes in many forms that suit different functions and made from various materials. The materials used vary from standard material to heat resistant material that can stand a temperature above 100 C
Seal hydraulic comes in many shapes and forms, and usually, each manufacturer uses a different type from the other. There also various materials used depend on the type of load of the hydraulic and application of temperature. For standard usages, materials that are commonly used are: poly Urethane (PU), Nitrile Rubber (NBR), Hydrogenated Rubber (NHBR), Ethylene Propylene Rubber (EPDM), Fluorine Rubber (FR) and many more special or hydraulic This is important to know as to know how to choose a hydraulic seal.
For hydraulic seals applications that operate at high temperatures (in hot areas such as around foundries and furnaces), hydraulic seals come in various materials. The materials used are usually made with; HNBR materials that can stand high temperature up to 135 degrees Celsius or hydraulic seal using EPDM materials
That can hold up to 150 degrees Celsius, can also be used, then there are FKM materials that are capable to operate at high temperature up to 200 degrees Celsius, and PTFE (Polytetrafluoroethylene) material which can stand extreme temperatures and capable to operate at temperatures up to 260 degrees Celsius.
The following are the forms and types of seal hydraulic adapted from the Sakagami seal catalog. However, for applications with higher pressure, V-Packing types are used for both rod seal and piston seal depending on the needs. The stacked V Packing made the seal be more durable, but it is more expensive than other types.
Aside from that seal type, there is another cylinder equipped with O-ring which functions as a static seal to prevent leakage of fluid (air or oil) from the parts connected to the cylinder such as the cylinder tube with end cup, cylinder tube with head cylinder or piston with a rod.
On the other hand, for a cylinder with longer stroke, it usually equipped with a wear ring that serves to maintain the stability of the movement which functions as a sliding bearing. In its practical applications, the original Cylinder hydraulic is often modified to reduce the maintenance costs. This happens, because seal kit is hard to obtain and/or the original cylinder hydraulic used does not compatible with its application and resulted in a cylinder underperforming most of the time.
In this case, it is better to replace the original seal (standard seal in the cylinder) with seals in the Indonesian market. The seal replacement can also reduce the maintenance cost and in some cases can increase the cylinder performance, because the standard seal is usually adjusted to where the cylinder is made.
Many cylinders, which are made in Europe or the USA, used a seal with their respective country’s standard which made finding replacement for cylinder seal quite difficult. European or American brand seals are hard to find in Indonesia except those manufactured by Hallite, and even so certain types, the market usually has no stock and be indent for up to 3 months. The brand parker which already established itself in the Indonesian market for quite long, the seals manufactured by parker are still difficult to acquire because of the same reason, no stock and have to indent.
Because of the high cost and long delivery time, a number of custom modification part is made and suited with stock in Indonesian market as replacement for the brand and type that are hard to acquire. The modification must be done with first observing some aspects, such as the seal material, seal mode, seal type, etc. If done properly, the modification can maintain the performance, e.g. the amount of pressure and resistance of the seal. Modifications should be made with little to no changes on the dimensions of the seal holder both on the piston mount and head cylinder.
In reality, when many changes are done to the size of the rod piston, it could cause deformation or defect. The rod piston or cylinder tube is usually repaired through grinding and through re-hard chrome or by honing the cylinder tube. Even, repair to rod piston or cylinder tube is done to reduce cylinder maintenance cost, a fatal error could occur when changes to the diameter dimension to the rod or cylinder tube is made too excessive. Because, even after hard chrome has been done, the rod or tube would not reach the default size. Then, changing the size (dimension) of the seal hydraulic diameter is inevitable.
By doing modifications, through these steps, instead of reducing maintenance costs, the cost could end up to be more expensive. Because, every time the seal kit is replaced over time, the replacement will be a custom made/special order because the size of the cylinder tube or rod piston already changed.
For consideration, the cost of a nonstandard seal or custom made/special order seal will be expensive and to manufacture the seal is very time-consuming. In addition, aside from the high price of special order seals, another matter to take into consideration is, the dimension of the special seal is usually done through the machining process and not through the molding process.
This resulted in the dimension of the seal is less accurate, because of miscalculation on the machine or human (human error and machining precision). Also, as a user, we will never know the quality of the material, because the quality of the material used is only known by the manufacturer.
That is why, when a problem is found in the rod cylinder or cylinder tube, which when repaired could cause extreme change to dimension, it is recommended to replace the rod cylinder or tube cylinder because it is safer and cheaper on overall maintenance cost.
Types of Hydraulic Seal (Seal Kit)
In this section, we will discuss the types, variation, and shapes of seals, and also functions of the seals that manufactured by Sakagami (Japan) dan Hallite (Europe)
- Piston Seal
- Rod seal
- Dust seal
- O Ring and wear ring
The dimension of the Piston seal is identical with the size of the cylinder (bore size), where dimensions diameter of seal that needs to be considered are outside seal diameter because this refers to the size of the diameter of cylinder tube,. Then followed by inside diameter and height of the seal refer to piston dimension as its mounting. Products made by Sakagami the piston seal models vary in:
- GPY Seal
This model has a dimension with a diameter ranging from 32mm to 250mm. GPY Seal model or commonly referred as GPY Packing, has standard material (RN919) made from Nitrile Rubber (NBR) with 85 Hs hardness and tensile strength 175 kgf/cm2, also with working temperature ranging from -30 to 100 C and most suitable for mining or excavating oil mineral
- RGY Seal
GPY seal model or often referred to as GPY Packing is using standard material (RN923) made from Nitrile Rubber (NBR) with a hardness of 85 Hs and tensile strength of 140 kgf/cm2, and working temperature of -30 s/d 100 C. It is very suitable for an operation that uses mineral oil fluid.
More information about size and types of Sakagami seal both seal hydraulic and seal pneumatic, click on seal Sakagami on type of seals section and the bottom of this article.
Seal installment of a head cylinder and piston-cylinder, also O-ring, seems easy, yet many maintenance operators do not understand this properly. This causes reduced resistance to the seal. Even, when not properly installed, leakage will happen and it will not perform as expected in its first use.
This happens due to the direction of the profile seal might be reversed or defect/deformation on the profile seal. Do not rush and take your time. Because installment of some specific seals could break your machine because the material is not elastic and placement position is difficult (narrow gap).
Aside from seal hydraulic, leakage also often caused by the careless installment of the O-ring. This cause the O-ring shifted and stuck, and worse, it could cause the O-ring to snap. Keep in mind, not every seal installment is difficult and needs to use the equipment, like rope (rope with plastic material is recommended) and clamp, especially when sliding a piston inside a cylinder to avoid damage to the profile seal.
One simple thing that neglected most of the time, but can affect the lifetime of the seal, piston rod and cylinder tube is sanitation problem. Because of this, make sure the component parts of seal hydraulic, cylinder tube and rod piston are clean from dust, dirt, scrap, etc. before installing. If there is any dust, dirt, or scraps enter the cylinder or stuck in the seal lips, it can cause leak for a long period of time.
Below are some types of seal
1. Sakagami Seal
2. Hallite Seal
3. Seal Parker
4. NOK Seal
5. Meiwa Seal
6. National seal
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