How To Install And Operate And Maintenance The Dry Gas Seal

Instruction Manual for Dry Gas Seal Installation, Operation and Maintenance

Overview Of Dry Gas Seal

Dry gas seal is a new type of non-contact shaft seal. It was developed based on the concept of gas lubricated bearings in the late 1960s, of which spiral groove seals are the most typical. After several years of research, the American John Crane Company took the lead in launching dry gas seal products and putting them into industrial use. It is suitable for any gas conveying system and is currently used more and more in imported devices in my country's petrochemical, oil refining, chemical, pharmaceutical and other industries. Practice has shown that dry gas mechanical seals are superior to ordinary contact mechanical seals in many aspects. Because they are non-contact seals, they are basically not limited by PV value. Compared with ordinary contact mechanical seals, it is more suitable as a shaft seal for large centrifugal compressors under high speed and high pressure. And it does not require sealing lubricating oil, and the gas control system required is much simpler than a contact-sealed oil system. The emergence of compressor dry gas seal is a revolution in seal technology. It changes the traditional sealing concept, organically combines dry gas seal technology and blocking sealing principles, and replaces the traditional "gas sealing liquid or gas sealing gas" with the new concept The concept of "liquid sealing gas or liquid sealing liquid" can ensure that any sealing medium can achieve zero

escape, which makes it also have broad application prospects in the field of pump shaft seals.

Dry Gas Seal Advantages

• The sealing oil system and the additional power load used to drive the sealing oil system are eliminated

• Unplanned maintenance costs and production shutdowns are significantly reduced

• The possibility of oil contamination of process gas is avoided

• Sealing gas leakage is small

• Low maintenance cost and good economical practicality

• The seal driving power consumption is small

• Long sealing life and reliable operation

Dry Gas Seal Working Principle

Compared with ordinary mechanical seals, dry gas seals are basically the same in structure. The important difference is that one of the dry gas seal seal rings is processed with evenly distributed shallow grooves. During operation, the gas entering the shallow tank is pressurized shrink, forming a local high-pressure area between the sealing rings, causing the sealing surface to open, so that it can operate in a non-contact state.

Achieve sealing

The following takes a typical spiral groove dry gas seal as an example for a brief explanation.

Figure 1 shows a schematic diagram of the sealing end face. A certain number of spiral grooves are processed on the sealing surface, and their depth is within 8~15μm. The main principle of sealing work is the balance of static pressure and fluid dynamics. 

Hydrostatic force is generated by medium pressure and spring force, and exists both when rotating and stationary. Hydrodynamic forces only occur when the seal rotates. When the seal rotates, the viscous shear force generated by the moving ring drives the sealed gas into the spiral groove. From the outer diameter to the center, the radial component flows toward the sealing dam, and the sealing dam controls the flow of gas to the low-pressure side, so the gas is compressed. , the pressure increases, the sealing surface separates, and an air film of a certain thickness is formed. The opening force formed by the air film force and the closing force formed by the spring force and medium force reach a balance, so the seal realizes non-contact operation. The air film formed between the sealing surfaces of the dry gas seal has a certain positive stiffness, which ensures the stability of the seal operation and can also lubricate the friction pair. In order to obtain the necessary fluid dynamic pressure effect, the dynamic pressure groove must be opened at a high Press side

For different working conditions, different dry gas seal overall structural forms can be adopted. In practical application, dry

Air seals mainly have three structural forms: single end face, double end face, and tandem seal.

In order to ensure the reliability of dry gas sealoperation, each set of dry gas seals has a matching monitoring and control system, so that the seal works in the optimal design state. When the seal fails, the system can immediately alarm, which is beneficial to maintenance workers.

People handle on-site incidents as quickly as possible. The dry gas seal monitoring system monitors whether the seal is operating normally by monitoring the amount of gas leakage.

If the gas leakage is too low or too high, the system will alarm, reminding the operator to check whether the control system pressure is within the design range. When the gas leakage exceeds a certain value, it indicates that the dry gas seal has failed and the system will interlock. Stop the vehicle to ensure that the equipment is not damaged.

Installation and removal of  Dry Gas Seal

Dry gas seals are precision components. Improper installation and disassembly can easily cause damage to the seal or shorten its service life.

The first installation of this dry gas seal must be carried out by our company’s professionals to the site for guidance.

The seal is divided into two parts: the seal body and the comb seal (maze seal). The seal body has a modular structure, and the dynamic and static parts are connected together through the mounting plate. It does not need to be disassembled during installation, and can be directly installed from the shaft end as a whole. Into the unit casing, and then remove the mounting plate. The installation is simple, reliable and accurate in positioning.

Inspection of seal before installation

If the dry gas seal has been stored for a period of time before use, the seal must be rotated and floated before installation.

Mobility check.

 1. Remove the storage and transportation protective cover 28.

 2. Place the seal on a clean assembly plate with the mounting plate (key 30) facing upwards, and remove the mounting plate.

 3. Turn the sleeve (item 20) according to the rotation direction marked on the outside of the seal. If it can rotate freely, it is considered qualified. 

If you feel that the rotation is blocked, it may be that water vapor or oil film has accumulated on the sealing end, and it needs to be disassembled for cleaning.

4. Use both hands to gradually and evenly press down the bushing until it stops moving. At this time, the lower sealing spring is

To compression, the spring of the upper seal is unloaded.

 5. Release your hands quickly. If the shaft sleeve can quickly follow and bounce back to the starting position, it can be considered to be floating. If it pops up slowly or fails to pop up, the seal should be disassembled for further inspection.

 6. Then use both hands to pull the shaft sleeve upward evenly (in the opposite direction to 1.4). At this time, the spring of the upper seal is compressed and the spring of the lower seal is unloaded. Quickly release your hands. If the shaft sleeve can quickly bounce back to the starting position, it can be considered that the float is normal. If the pop-up is slow or unable to pop up, the seal should be disassembled for further inspection.

 7. After the inspection is completed, reinstall the mounting plate.

Preparations Before Installation

 1. Before installation, the sealing gas, isolation gas, and pre-gas pipelines should be thoroughly purged. The purging gas must be dry.  Clean and dry, no particulate impurities or oil are allowed inside the pipeline.

 2. Thoroughly clean the surface of the cavity and shaft through which the seal is installed, and there must be no particles, impurities, rust spots, Oil stains, etc.

 3. Carefully check the edges of the cavity and shaft through which the seal is installed. Sharp edges should be blunted, and there should be no burrs on the surface. Defects such as thorns and scratches.

 4. Carefully check the O-rings on the outside of the sealing shell and inside the shaft sleeve. If there are any defects, replace them in time.

 5. Adjust the axial position of the main shaft to the working state, carefully measure the relative positional relationship between the positioning steps of the seal housing on the unit cavity and the positioning steps of the seal sleeve on the main shaft, and follow the installation dimensions 37.5 required on the seal assembly drawing. mm (frame size) Calculate the required thickness of the adjustment ring (item 27), re-process and adjust it randomly The thickness of the entire ring meets the requirements for on-site use. To ensure that the actual installation dimensions of the seal meet the design requirements.

 6. Confirm that the rotation direction marked on the seal housing is consistent with the rotation direction of the spindle.

 7. Since the bearing bush needs to be removed when installing and disassembling the seal, special tools must be used to fix the shaft in the central position (special tools such as horse racks are provided by the factory). This special tool should be used when installing the seal and after installing it on the shaft. The tool keeps the spindle in the center position and can only be removed after the bearing bush is replaced.

 8. Apply a small amount of silicone grease appropriately on the outer surface of the O-ring. Be careful not to use butter or other lubricants. Excess silicone grease should be wiped off to prevent lubricant from entering the seal area during seal installation

 Installation of Dry Gas Seal

Note: During the installation process, determine when it is necessary to remove or install the radial bearing bush and fixed bearing according to the actual situation.

The axial and radial position of the stator and rotor.

 Before installing the seal, please note that the connection holes on the gland should correspond to the 8 M12 screw holes on the chassis. Carefully and slowly install the complete set of seals with the mounting plate from the end of the main shaft. Gently push the seal into the machine by hand.The group housing is about 10mm. Note that the seal cannot be rotated during this process.

1. Use the installation tool provided in the supplied spare parts to install the dry gas seal into the seal cavity of the unit.

2. Assemble the installation tools as shown in Figure 4 (2 sets in total);

3. Pass the two M12 studs through the connection holes on the dry gas seal casing and screw them into the M12 screw holes of the unit casing (two

The root studs are distributed at 180°in the circumferential direction);

4. Slowly rotate the two nuts symmetrically and evenly, and push the dry gas seal into the unit cavity.

5. After pushing the dry gas seal into the unit cavity, remove the installation tools and keep them properly (it is also necessary to remove the dry gas seal) to use this tool).

6. Use 8 M12×25 hexagon socket screws (item 11) to fix the dry gas seal in the seal cavity of the unit.

 7. Remove the mounting plate (Item 30), install the locking nut (Item 19), and pass the dry gas through the adjustment ring (Item 27) The sealing sleeve is pressed against the shaft shoulder.

Note: To prevent loosening, a small amount of anti-loosening glue (Loctite 222) can be applied to the threads.

8. Install the comb tooth holder (Item 13) and tighten the connecting screws (Item 18).

9. Install the comb ring (Item 14) and tighten the connecting screw (Item 16).

10. Check the relevant installation dimensions according to the rotor position to determine whether the seal is in place. If correct, install additionally At one end, if there is a problem, check and analyze the cause immediately.

11. Repeat the above steps to install the seal on the other end.

Disassembly of Dry Gas Seal

1. Remove the screws (Item 18), and take off the comb tooth holder (Item 13) and comb tooth ring (Item 14)

2. Loosen and remove the locking nut (item 19)

3. Fit the mounting plate (key 30)

4. Remove the dry gas seal connecting screws (item 11)

5. Use the two M12 studs provided with the machine to screw into the M12 screw holes on the dry gas seal gland, and secure the entire set of dry gas seals. Cap the unit cavity.

6. Carefully remove the complete set of seals from the shaft end.

Note: The removed dry gas seal must be placed in a clean plastic bag to be airtight and dust-proof, and then placed in a sealed packaging box.

 Operation and Maintenance of Dry Gas Seal

 Dry gas seal start-up procedure

1. Start the dry gas seal control system according to the dry gas seal control system commissioning procedure.

2. Make sure that all instrument indications and remote transmission signals on the system are normal before inflating the process pipeline.

3. Put the unit’s lubricating oil system into service.

4. Start the compressor unit.

Note: The unit's lubricating oil pump must not be started before the dry gas seal isolation gas is introduced!

Maintenance During Dry Gas Seal Work

The dry gas seal design has a wide application range and requires no maintenance under normal circumstances. Generally, the amount of sealing gas leakage should be observed every day. If the leakage of sealing gas increases, it may indicate the possibility of seal failure. Usually should

Note the following points:

 1. The dry gas seal rotates in one direction, and reverse rotation is absolutely prohibited. At the same time, it should be avoided when the speed is less than 5m/s Run at low speed for a long time. Both situations have the potential to damage the seal.

 2. Ensure the flow of sealing gas is stable. Maintaining stable and uninterrupted sealing gas is a basic condition for the normal operation of dry gas seals. If the nitrogen pressure is insufficient, close attention should be paid; if the nitrogen bottle needs to be used, a dedicated person should monitor it at any time. control to ensure continuous supply of gas.

 3. Avoid negative pressure operation of the seal. Back pressure will cause a substantial increase in leakage under static pressure conditions, and It will cause damage to the sealing face during operation.

 4. Monitor changes in seal leakage at any time. Changes in leakage directly reflect the operating status of the dry gas seal. There are many factors that cause changes in leakage, such as fluctuations in process media, shaft channeling, surge, changes in pressure, temperature and speed, etc. As long as it does not continue to rise, the seal is considered to be operating normally; however, if the leakage amount is abnormal A continuously rising trend indicates a failure of the dry gas seal.

 5. When the filter pressure difference reaches the alarm value, the filter should be switched in time and the filter element should be replaced.

 6. When the unit is stopped, you must wait for the unit to completely stop running and stop the lubricating oil system for more than 10 minutes. Only then can the dry gas seal control system be turned off.

 Shipping And Storage Of Dry Gas Seal

The complete set of seals should meet the requirements for transportation and frequent handling. Generally, it should be placed in a specially manufactured strong wooden box and fixed with foam plastic limits. Other loose parts in the box must be safely packed and placed on the shaft

space in the sleeve to prevent damage during transportation.

In addition to the need for installation, the use of mounting plates also plays an important role in preventing relative collision between the sealing housing and the rotor during transportation. Therefore, as a complete set of dry gas seals, it is necessary whether it is transported or stored. Place the mounting plate in place.

The indoor temperature of the sealed storage room is preferably between 15 and 25°C, and it should be kept away from heat sources such as boilers, heat exchangers or direct sunlight. The ambient humidity should be less than 75%. It is recommended to place a pack of desiccant in the packaging box.

To ensure waterproofing, use oiled paper or cloth to package and seal. If it will not be used for a long time, it should be wrapped and sealed with polyethylene film.

If the seal is shut down in the compressor for more than 60 days, it should be noted that the seal end face may be invaded by oil. You can usually check whether there is oil in the dry gas seal isolation gas inlet pipeline, or try to turn the car manually. If there is oil or

If turning is difficult, professionals should dismantle the seal, inspect the end face and clean it.

Since the dry gas seal is a precision-made high-speed rotating component, the assembly relationship is complex and must be processed before leaving the factory. Strict dynamic balancing experiments and operation experiments have been carried out. Therefore, non-professionals must not disassemble and disassemble it at will.

If the compressor is shut down for a long time with a dry gas seal, the main shaft should be fixed to prevent movement and possible damage to the seal. After confirming that the environment in the unit is dry, seal all connections on the compressor and do not allow

The remaining oil and other impurities in the unit may come into contact with the dry gas seal.

If the dry gas seal exceeds the normal service life, some parts such as rubber parts, springs, etc. need to be replaced and regular inspections must be performed.  The service life of the dry gas seal is related to the storage time, operating time and the operating status of the unit. If the storage conditions are good and the unit operates well, the seal can be stored for 3 years and operated continuously for more than 3 years. However, the storage conditions are not good, or the unit starts and stops frequently, Vibration of the unit, shaft channeling, excessive beating, unclean pipes, etc. may cause the sealing life to be shortened.