DMS SEALS TECHNOLOGY CO.,LIMITED
The Professional Sealing Solution Supplier.
Scraper seals, widely known as wiper seals, play a pivotal role in the protection of hydraulic cylinders. It is said that dynamites come in small packages. This is particularly true for scraper seals as their size may often cause them to be judged as "one of those car parts", yet their function is as important to the proper functioning of the hydraulic cylinders as any other seal. As part of the sealing array of hydraulic cylinders, they are installed to prevent contaminants from coming into contact with the piston rods of the hydraulic cylinder as they disavow into the system. Dust particles, moisture, weld flash, and metal chips are the most likely contaminants which may cause the malfunctioning of the hydraulic cylinder, and as such, measures need to be taken to ensure that they are always in proper function.
Not only do the wiper seals prevent foreign entities from entering the hydraulic cylinder, but they also guard against the loss of hydraulic liquid from the hydraulic cylinder. This double impact of the wiper seals ensures the proper functioning of the whole system. To ensure optimum quality, and function, they often undergo a number of quality tests, such that when you as a consumer buy the product, you are much satisfied with its function.
Scraper seals come in different shapes and sizes depending on the hydraulic system in which they are going to be used. The main component used in manufacturing the seals is polyurethane(TPU). Many modern-day wiper seals are manufactured from TPU which makes them flexible but strong at the same time. The polyurethane in the seal gives it its wear resistant properties which in turn play a very vital role in the hydraulic cylinder. The wear resistance means that the scraper seals are strong enough to create a long-lasting barrier against foreign substances. This also means the seals are resistant to damage from friction and therefore will, by all means, prevent loss of the hydraulic liquid from the cylinder.
Some wiper seals are made from rubber elastomers which have the ability to trap small particles like dust particles which are airborne. In other terms, they have "trapping" properties which enable them to carry out this function without fail. A number of other materials with their different properties are also included in the manufacture of wiper seals. These other materials include Buna, Viton, PFTE, Silicone, and EPDM.
There are two major types of scraper seals namely, the press-in wiper seals and the snap-in wiper seals. Each one of these is designed to suit the function for which it is intended perfectly.
Press- In Scraper Seals
Press-in wiper seals as according to their name are fitted into. The hydraulic cylinder by pressing them into the housing on the cylinder head. There are various types of these seals which are designed to function in their intended different hydraulic cylinders.
PA - This is a polyurethane based wiper seal with a single lip design furnished with a steel retaining ring. They have a single wiping lip projecting from the head of the cylinder. The design of the PA makes it effective in the reduction of contaminants that might adhere to the wiper lip.
MCW -These also have a single wiping lip, however, unlike the PA scraper seal, it does not protrude from the head of the cylinder. This characteristic of the seal makes it specialized for its function in that it permits a compact arrangement when the cylinder disavows thereby leaving no room for entry of any foreign substances into the cylinder.
PAD and PADV -These are double lipped scraper seals which have one of their wiper lips facing the inner part of the hydraulic cylinder. As the rods retract, the seals regulate their lubrication, keeping them in function and also preventing external moisture from entering the cylinder. The other function of the internal lip is to get rid of excess fluid from the rod by allowing the fluid to return under the rod upon disavowing of the rod. In essence, the double lip wiper seals are more effective than the single lip seals.
Snap-In Scraper Seals
They are very easy to install. They do not have any metal in their design and also do not require any specialized equipment for their installation. However, one limitation that these wiper seals have is that with time, they become loose in the housing with results in poor functioning of the hydraulic cylinder. When it becomes loose, environmental contaminants can easily find their way into the hydraulic cylinder which therefore defeats the whole purpose of having a scraper seal. To ensure this doesn't happen, the snap-in wiper seals should be fitted with a special sealing and venting features in order to increase their effectiveness and also protect the hydraulic cylinder system.
DTW - These are also made from polyurethane, have a single lip design and a static seal lip on the outer surface of the cylinder. The static outer lip ensures tight sealing from the outer surface which acts as a shield against environmental contaminants. Not only does the wiper lip on the outer surface act as a shield, but it also keeps the wiper tight ensuring that it maintains its position in the housing.
The DX seals have an easily recognizable profile which has a single external wiper lip and an edge that is vented on the inner part. The DX wiper lip works for hand in glove with the O-ring which serves as an energizer. The O-ring also increases resistance from environmental contaminants such as moisture, dust and even snow by maintaining a robust static sealing effect.
HW - The function and design of the HW scraper seals are similar to those of the PAD and PADV. They are designed to have a double wiper lip with one of the wiper lips facing the inner part of the hydraulic cylinder. On the extending stroke, the internal wiper lip removes excess hydraulic fluid from the rod, and when the rod retracts, the excess fluid is made to go under the rod seal. Such wiper seals as these have a longer life span which means increased protection of the hydraulic cylinder.
Ultimately, it is important to ensure that the hydraulic system is functioning in its intended manner. The scraper seal is probably one of the most undervalued seals in the hydraulic system; however, it is paramount to note that it is as important in the hydraulic system as is any other another seal.