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 discussed in detail in this article.
Pump seals
Modern pumping equipment is completed with a large number of elements. At the same time, the specifics of the work require paying increased attention to the normal and uninterrupted functioning of the products as a whole. Due to its simplicity of design and ease of use, pump stuffing box seals are used much more often than other sealing devices.
Performance requirements
The impeller of all types of pumping equipment works thanks to the motor. Most often it is electric. Through a mechanical clutch, energy is transmitted from the motor shaft to the impeller, which sets it in motion. The shaft itself extends beyond the equipment housing, which makes the shell leaky. Therefore, the loss of working fluid is inevitable.
If, however, the pump seals are used, leakage of the pumped liquid can be avoided. The following technologies are used:
- Packed (gland) seal. It is a ring of fibrous material.
- Cuff. Elastic materials are used for this sealing, which can be reinforced to increase rigidity. Used for installation in pumping equipment with low shaft speed.
- End. It consists of two rings, closely spaced to each other on the shaft. One of them rotates with the shaft, while the other remains completely stationary.
- Slit. The second name is labyrinthine. It is considered the most reliable modern type of seal. Presented in the form of a soft alloy ring. Used in multistage pumps where the use of other technologies can significantly affect efficiency.
In addition, there are devices that do not require seals, such as wet rotor magnetic drive pumps.
Description of stuffing box seals
Slotted materials are most commonly used to seal submersible pumps. They do not have special requirements for leakage of liquids. The duration of operation plays a big role here.
Sealing pump stuffing boxes appeared almost at the same time as the equipment for pumping liquids. These are kind of rings.fibrous material, which are in the stuffing box, hence their name. The packing must be wetted by the liquid transported through the pipelines. This is necessary to cool and lubricate the stuffing box. Wetting itself is fraught with fluid loss. An hour of pump operation assumes a loss of 1-15 liters of water. If the packing is not wetted, then the material will lose its usefulness, it will quickly “burn out”.
Oil seals need constant maintenance. In this case, compressors and pumps can not be disassembled, which is one of the significant advantages of seals. Self-service is a periodic “pull-up” of the cuff.
Typical seal variations for pump equipment
The modern market offers various seals for pumps; typical oil seals come in two main types:
- Reinforced packing with one edge. The main purpose is to prevent the loss of the pumped liquid.
- Cuffs reinforced with anther and one edge. Used to protect the connection itself from dust and dirt. Also do not allow liquid to leave the conveying system.
If we consider the production method, 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 rubber. Products are made from1, 2 and 3 rubber classes. They are characterized by a relatively high negative operating temperature threshold (-30, -45, and -60 °C, respectively).
- Fluoroelastomer based. Raw material - rubber groups 1 and 2. When pumping mineral or gear oil, they can withstand temperatures up to 170 ° C.
-
Made of silicone rubber. In the manufacture of rubber used exclusively 1 group. 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 stuffing box if it is intended to work with a shaft up to 20 mm or more than 120 mm.
Stuffing box packing: performance properties, for which pumps it is better to use
As a rule, cuffs differ from other seals in their flexibility, plasticity. High wear resistance is also a significant advantage of the products. Minor impact on the shaft expands the application segment.
Performance characteristics directly depend on the structure of the sealant and the composition that was used in production. Depending on the weave, there are diagonal (through and combined) glands and single-layered (meaning the structure of the core). The composition of the cuffs are:
- asbestos and non-asbestos;
- dry and impregnated (fatty, graphite and adhesive mixtures are used as impregnation);
- reinforced and non-reinforced.
Oil seals are used to seal the connection of centrifugal, piston pumps and hydraulic presses. The packing can also be used in plunger equipment for pumping liquid media. When installing the product, keep in mind that pumps with gland seals will pass a certain amount of liquid mentioned above.
Graphite-ceramic seals
This is one of the types of cuffs 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 seals used? There are not many water pumps suitable for mechanical seals. As a rule, the application segment is limited only to surface mechanisms.
Service life can reach 10 years. In this case, it is worth adhering to the correct operation of the pumping station. The main requirements put forward at the time of operation of the equipment:
- No "dry run". 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 oil seals for water seal pumps
Cuff equipment forpumping water looks like braided lacing with a square section. Asbestos (cotton or bast) thread may have inclusions of copper or brass wire. Water seal pumps have a core made of lead. Tape size 50.5. 4 lead wire braid can be used instead.
Water sealed seals are used, usually on the suction side. But it is possible to use them from the opposite side. The packing size is directly related to the shaft diameter. The maximum number of seal rings is 5.
How to choose an oil seal
Selection of seals is carried out according to a number of characteristics. Undoubtedly, the most important issue is reliability. Among other important criteria, cost is considered. Additional parameters that are taken into account when choosing devices:
- number of operating hours;
- fluid loss;
- expiration date;
- costs that will be incurred in case of repair.
In addition, the selection of seals for pumps is carried out taking into account standard sizes. These include outer and inner diameters, base height and thickness.
What consumers are saying
Many people have already encountered the installation of an oil seal for a single-stage pump. The versatility of stuffing is often noted. The use of seals is not limited to high speed shafts.
It is noted that the stuffing box seal of pumps with silicone-based lubricantshows great thermal stability.
High carbon variations significantly reduce the expansion ratio as the temperature of the pumped liquid increases. And aramid fibers with special PTFE impregnation allow the stuffing box to work in aggressive environments in the chemical industry, thermal power plant and in the paper industry.
