In industrial production during the operation of pipelines, various types of pumps , losses of pumped liquids inevitably occur. Numerous seals serve to prevent these cases, one of which will be considered in detail in this article.
Gland seal
Modern pumping equipment is equipped with a large number of elements. In this case, the specifics of the work requires paying increased attention to the normal and uninterrupted functioning of the products as a whole. Due to the simplicity of its design and ease of use, pump packing seals are used much more often than other sealing devices.
Operational requirements
The impeller of all types of pumping equipment works thanks to the motor. Most often it is electric. Through a mechanical coupling, energy is transferred from the motor shaft to the impeller, which sets it in motion. The shaft itself extends beyond the equipment enclosure, which makes the enclosure leaky. Therefore, loss of working fluid is inevitable.
If you use a pump seal, leakage of pumped liquid can be avoided. The following technologies are used:
Stuffed (stuffing box) seal. It is a ring of fibrous material.
Cuff. For such a seal, elastic materials are used that can be reinforced to increase rigidity. It is used for installation in pumping equipment with a low shaft rotation speed.
End face. Consists of two rings tightly located to each other on the shaft. One of them rotates with the shaft, and the other remains completely stationary.
Slotted. The second name is labyrinth. It is considered the most reliable modern type of seal. It is presented in the form of a ring of soft alloy. It is used in multistage pumps, where the use of other technologies can significantly affect the efficiency.
In addition, there are devices that do not require seals, such as magnetic clutch pumps and wet rotors.
Description of stuffing box seals
Slit materials are most often used to ensure the tightness of submersible pumps. They do not have special requirements for fluid leakage. Here, the duration of operation plays a large role.
Pump packing seals appeared almost at the same time as the liquid pumping equipment itself. This is a kind of ring made of fibrous material, which are located in the stuffing box, from where their name came from. The packing must be wetted by the fluid transported through the pipelines. This is necessary for cooling and lubricating the oil seal. Wetting itself is fraught with loss of fluid. An hour of operation of the pump involves the loss of 1-15 liters of water. If the packing is not wetted, then the material will lose its usefulness and will quickly “burn out”.
It is necessary to constantly maintain the seals. Compressors and pumps can not be disassembled, which is one of the significant advantages of seals. Self-service is a periodic "pull-up" cuff.
Typical Seal Variations for Pumping Equipment
The modern market offers various pump seals; Typical oil seals are represented by two main types:
Reinforced padding with one edge. The main purpose is to prevent the loss of pumped liquid.
Cuffs reinforced with anther and one edge. Used to protect the compound itself from dust and dirt. Also do not allow fluid to leave the transportation system.
If we consider the method of production, then we can distinguish oil seals:
with molded edge;
with machined edge.
Depending on the type of rubber used, there are such cuffs:
Based on nitrile butadiene rubber. Products are made from 1, 2 and 3 classes of rubber. They are characterized by a relatively high threshold for negative operating temperatures (-30, -45, and -60 ° C, respectively).
Based on fluororubber. Raw materials - rubber groups 1 and 2. When pumping mineral or gear oil withstand temperatures up to 170 ° C.
Made of silicone rubber. In the manufacture of rubber only 1 group is used. The lower limit of the operating temperature of the packing is -55 ° C.
As a rule, modern cuffs come with springs. They are suitable for sealing on shafts of different diameters.
The spring can be supplied separately from the gland if it is intended to work with a shaft of up to 20 mm or more than 120 mm.
Stuffing box: operational properties, for which pumps it is better to use
As a rule, cuffs differ from other gaskets in their flexibility and ductility. High wear resistance is also a significant advantage of products. A slight impact on the shaft expands the application segment.
Operational characteristics directly depend on the structure of the sealant and the composition used in the production. Depending on the weaving, there are diagonal (through and combined) glands and single multilayer (meaning the structure of the core). The composition of the cuff is:
asbestos and asbestos-free;
dry and impregnated (fat, graphite and adhesive mixtures are used as impregnation);
reinforced and unreinforced.
Oil seals are used to seal the connection of centrifugal, reciprocating pumps and hydraulic presses. Stuffing can also be used in plunger equipment for pumping a liquid medium. When installing the product, do not forget that pumps with stuffing box seals will allow a certain amount of liquid to pass through, mentioned above.
Graphite-Ceramic Seals
This is one type of cuff for pumping equipment. The use of this type of seal completely eliminates the ingress of working fluid into the equipment motor. Where are graphite-ceramic seal packing used? There are not so many water pumps to which the mechanical seal fits. As a rule, the application segment is limited only to surface mechanisms.
Service life can reach 10 years. At the same time, it is worthwhile to adhere to the proper operation of the pumping station. The main requirements put forward at the time of equipment operation:
Lack of "dry running". It is strictly forbidden to keep the pump in the “on” mode if there is no liquid in the system.
It is best to pump the most purified substance. The presence of impurities shortens the life of the cuff.
Be sure to adhere to the temperature regime.
Advantages of glands for water-sealed pumps
The cuffs for the water pumping equipment look like a square braided lacing. Asbestos (cotton or bast) thread can have inclusions of copper or brass wire. Water-sealed pump oil seals have a lead core. The size of the tape is 5 * 0.5. Instead, weaving with 4 lead wires can be used.
Glands with a water seal are used, usually on the suction side. But their use from the opposite side is not excluded. The size of the packing is directly related to the diameter of the shaft. The maximum number of seal rings is 5.
How to choose an oil seal
The selection of seals is carried out according to a number of characteristics. Without a doubt, the most important issue remains reliability. Among other important criteria, cost is considered. Additional parameters to consider when choosing devices:
In addition, the selection of seals for pumps is carried out taking into account the sizes. These include external and internal diameters, height and thickness of the base.
What consumers say
Many have already encountered installing an oil seal for a single-stage pump. Often, the versatility of packing is noted. The use of gaskets is not limited to high speed shafts.
It is noted that the seal of the pump oil seals with silicone-based lubricant exhibits greater thermal stability.
Variations with a high carbon content significantly reduce the degree of expansion with increasing temperature of the pumped liquid. Aramid fibers with special PTFE impregnation allow the stuffing box to work in an aggressive environment in the chemical industry, thermal power plants and in the paper industry.