How to prevent internal leakage in valves

For relatively important valves, or when the incoming material contains impurities, it is advisable to install a line filter in front of the valve. The removal of impurities is usually done through flushing; if that doesn’t work, the equipment has to be taken offline for repair

Internal leakage is a common problem with valves; there are no valves that are completely leak-free. Even high-quality shut-off or control valves, those with a leakage level of VI, cannot be guaranteed to be leak-free over time； For media that contain impurities or are prone to solidification, it is not recommended to use globe valves; gate valves or ball valves are preferred. If the impurities are quite hard, it is advisable to install a pipe filter with an appropriate mesh size in front of the valve. Of course, over time, if internal leakage becomes severe, it will be necessary to replace the valve as well, haha

Internal leakage is a long-standing problem; a filter can be installed. In particular, it’s essential to clean the system thoroughly right after starting the vehicle, otherwise it will be troublesome if debris remains in the system

The last edit to this post was made by 020222 on 2009-9-4 at 13:39. As is well known, packing is the sealing material used in dynamic seals; it fills the space within the valve packing box to prevent the medium from leaking through the valve stem and that space. The service life of a valve often depends on the service life of its sealing surfaces and packing system. Valves have four main requirements for gaskets: ① Corrosion resistance ； ②Good sealing performance ； ③Low coefficient of friction ； ④Low corrosivity (corrosion inhibitors must be added to graphite asbestos rope gaskets for corrosion protection). 　　Leakage at the valve packing is the most common and hardest-to-overcome fault in various devices. For valves with severe leakage at the packing area, the valve stem shows considerable wear after disassembly; the main reason for this is that the packing is irregular in shape, rough, and has high hardness ； At the same time, there are also: ① Rough machining of the inner wall of the stuffing box, resulting in leakage of the medium outward ； ②The valve stem lacks sufficient stiffness; closing the valve forcefully can cause it to bend, leading to leaks ； ③The valve stem has low precision, excessive surface roughness, and its material is not resistant to corrosion by the medium ； ④Incorrect method of installing or removing the packing ⑤ The variety of packing is limited, failing to meet the requirements of the operating conditions ； ⑥The valve stem, stuffing box, and gland are not coaxial, resulting in the packing being compressed unevenly. These issues collectively reflect design and manufacturing quality problems related to filler material selection, type selection, processing, and assembly. 　　At present, the sealing fillers used in our country have inherent weaknesses that cannot be overcome due to limitations in their material and structure. For example: 1) Cotton and linen fillers: although they possess good flexibility and elasticity, they offer little resistance to radial movement of the shaft. But it is not corrosion-resistant, nor can it operate under high temperatures and pressures; repeated tightening is required after assembly. Its scope of application is limited, and its uses are gradually declining. 2) Asbestos rubber packing: Although it can withstand certain temperatures and has a certain degree of pressure resilience, it tends to lose its crystalline water at high temperatures ； Rubber undergoes creep and stress relaxation when heated ； Not resistant to chemical corrosion ； The surface of the product is rough, resulting in a high friction coefficient ； Furthermore, asbestos contains carcinogens that are harmful to human health, and it has been completely banned. 3) Rubber and other polymer fillers: they tend to flow under high temperatures, are susceptible to corrosion by acids and bases, and are limited by temperature, resulting in a narrow range of applications. 4) PTFE filler: It has good chemical inertness, but suffers from the disadvantages of cold flow and thermal stress relaxation. 5) Flexible graphite packing rings: They have many advantages over the aforementioned packings, but they have low strength; the individual ring structure lacks versatility, and the procedures for supply and demand are complicated ； Production cannot be carried out through continuous automation, resulting in large fluctuations in quality. 6) Carbon fiber filler: Although it possesses high strength as well as good temperature and corrosion resistance, it has poor compressive resilience, and its fibrous structure makes leakage of the material inevitable. If other organic substances are used for impregnation to compensate for the aforementioned defects, the heat and corrosion resistance decreases significantly; moreover, the processing cost is high, the price of the resulting products is expensive, which limits their application. 7) Flexible graphite packing: It combines and retains the advantages of the aforementioned types of fillers, overcoming the disadvantages of traditional sealing fillers. It features resistance to high and low temperatures, good chemical inertness, thermal conductivity, no aging, self-lubrication, good compressive resilience, and excellent flexibility. By understanding the properties of the aforementioned packing materials, and by designing, selecting, and installing them in a rational and scientific manner based on factors such as the medium, temperature, pressure, and diameter, as well as the shape, specifications, quantity of the packing materials and their installation methods, it is possible to not only save significant amounts of material costs but also ensure the sealing performance of the valve and improve its quality. The design of the packing is a crucial issue that cannot be ignored. Through long-term research and development, four main principles for packing design have been identified: 1) Use retaining rings that are not prone to bending at both ends of the packing to prevent it from being pushed out of the packing area. Note that the retaining ring must meet two key requirements: first, it must have the proper fit precision with the valve stem, but it must not damage the valve stem ； Second, it must be less prone to bending than the packing itself, in order to transfer the load from the compression ring to the packing, while sufficient plasticity ensures that the packing material assumes a sealing shape. (The retaining ring required for special design depends on the type of valve and packing. ) 2) Use a valve stem bushing device near the packing to maintain the positioning of the valve stem. A packing system made of a plastic-grade material helps to keep the valve stem aligned. Most packing materials are plastic in nature; they are held in place by compressive rings that are not prone to bending, and these compressive rings are in turn held by very hard bushings. These bushings serve to maintain the coaxiality of the valve stem and to prevent the components inside the packing system from being compressed. 3) Use the minimum amount of filler to meet the sealing requirements, thereby minimizing the adverse effects of thermal cycling ； If the loss of packing material is the main cause of valve leakage, an excessive amount of packing will be used (our company uses as many as a dozen pieces of packing in the flat valves used for oil and gas). In fact, performance tests show that the use of excessive filler increases friction, which in turn leads to greater wear of the filler material, reduces its lifespan, and increases leakage at the valve stem. 4) A constant and appropriate packing pressure is applied using an elastic workload (this appropriate force depends on the type of valve and packing). 　　Under harsh operating conditions, when very low leakage is required, it is essential to apply an appropriate force on the packing through the workload. The packing is used in conjunction with a proper compression system, or the applied load is adjusted according to the packing system (type of packing, type of valve, and type of retaining ring); this workload has no impact on the rapid compression loss of the packing or on its service life. The workload can also mitigate the negative effects of thermal cycling; if there is still some compression capacity in the load spring, it can reduce some of the excess force generated by thermal expansion in the packing (but not all of it), as well as minimize compression losses. Regarding the polytetrafluoroethylene packing commonly used in valves for oil, chemical, and natural gas systems, the above four points are relevant: First, due to the tendency of polytetrafluoroethylene to undergo cold deformation, it is easier to be compressed than most other packing materials; therefore, retaining rings must be installed at both ends of the packing to prevent it from being pushed out of the packing area. After conducting performance tests using various retainer ring systems, it was proven that a system consisting of two retainer rings is very effective for restraining polytetrafluoroethylene packing. (The retaining ring is made of graphite filled with polytetrafluoroethylene. Secondly, the packing compression ring with a PTFE lining can also act as a substitute for a bushing to help maintain the coaxiality of the valve stem. 　　Thirdly, since the packing often expands and contracts during operation, the larger the packing ring, the more likely it is to expand and contract. A deeper stuffing box and a smaller stuffing ring design, on the other hand, can provide better sealing performance. At the same time, studies have shown that an inner cavity capable of holding 6 packing rings is the best choice, (with the two rings at the top playing a key role in sealing. ) Therefore, using a narrow lumen to insert 6 packing rings is the most effective structure for sealing the valve stem. 　　Fourth, polytetrafluoroethylene has a thermal expansion coefficient 10 times greater than that of steel, which increases the friction and compression losses of the filler during heat cycles. Applying a constant and appropriate packing pressure using a variable workload can mitigate the negative effects of thermal cycling. Furthermore, the shape design of the filler is also quite critical. As for PTFE packing, its shapes are mostly V-shaped and U-shaped; in the United States, butterfly-shaped types are also used. (But regardless of the shape of the packing, consistent coaxiality must be maintained among the valve stem, packing box, and packing gland during assembly. ) If the design of the packing meets the main principles outlined above, then even under harsh operating conditions, the designed packing will still meet the leakage standards, while other types of packing will fail. Furthermore, the packing gland is equally important in ensuring that the packing does not leak. The heart of the packing system is the packing box and the packing gland. Among them, the smaller and deeper stuffing box design provides better sealing performance ； As for the packing gland, some manufacturers use an open-type gland with union bolts for securing medium and high-pressure valves. Based on observations made at sites where valves used in the petrochemical industry are maintained, it can be seen that this type of open-type gland does not provide reliable sealing under high temperature and high pressure conditions. During operation of the valve, the packing gland is compressed on one hand by the pre-tightening force applied to the bolts, and on the other hand by the impact of the medium inside the valve body (transmitted through the packing). Under the influence of these two opposing pressures and high temperatures, the packing gland deforms (the edges of the packing gland, namely the opening areas, become skewed, the bolts come loose from the gland, resulting in leaks). To eliminate this leakage, I recommend that valve manufacturers switch from open-type packing glands to closed-type packing glands. That is, a gasket that does not have openings can be added on top of the packing gland using a padding method, or the two ends of the opening can be sealed by welding; in this way, even if the gland deforms, the bolts will not slip out. Thus, leaks at the packing area caused by deformation of the packing gland are eliminated. In addition to the design and selection of fillers, their processing, manufacturing, and filling assembly are also extremely important. The packing is the part of a valve that is most prone to failure, but analysis of most damaged packings shows that approximately 70% of such damage is caused by human factors. For example, the filler material is not selected appropriately ； Incorrect filling method ； Ignoring the correct procedures for assembly, etc. To eliminate these 70% of potential problems, proper installation of the packing and an understanding of the common issues that arise during its installation are essential skills that one must master. The most commonly used type of packing in valves is compressed packing, which consists of various materials combined together to form seal elements in rope, disc, or ring shapes, depending on the operating conditions ； Next is the flexible graphite filler. 　　The packing is a dynamic sealing mechanism installed between the valve stem and the valve cover packing box to prevent the medium from leaking out. Its proper installation should be carried out under the conditions that all components of the packing assembly are in good condition, the packing is pre-formed, and the valve stem is in good condition and in the open position (except during on-site repairs). ①Before installation, the asbestos filler without graphite should be coated with a layer of flake graphite powder; the filler must remain clean, and no impurities such as graphite or sealing grease should be present ； ②For valves in which packing can be fitted over the upper end of the valve stem, the direct fitting method should be used as much as possible. Before fitting it in, first remove the bracket, handwheel, handle, and other transmission components, and use a pipe that is higher than the valve stem as a pressing tool to compress the packing. For those that cannot be fitted directly, the packing should be cut in an overlapping manner (this method is applicable to flexible graphite packings, but is prohibited for herringbone packings and should be avoided for O-rings), with the overlaps offset vertically. Slide the packing around the valve stem at an angle, then move it up and down to align the cuts, and gently insert it into the stuffing box ； ③When installing the packing in the stuffing box, it should be placed layer by layer, with each layer being compressed evenly using a compressor. The overlapping positions of the cuts in each ring of the filler should be offset by 120° from one another ； When installing the first ring of packing, carefully check whether the bottom of the packing is flat and whether the packing pad has been installed. During the installation of the packing, the valve stem should be rotated every 1 to 2 turns to prevent it from getting stuck with the packing, which could affect the opening and closing of the valve. ④Once the stuffing box is almost filled, the packing should be compressed using the packing gland. When using the gland, apply even force; the bolts on both sides should be tightened symmetrically. Do not distort the packing gland, as this can lead to uneven pressure on the packing and friction with the valve stem. The depth to which the gland sleeve of the packing gland is pressed into the stuffing box should be between 1/4 and 1/3 of its height; alternatively, the height of one turn of the packing can be used as the depth for pressing it into the stuffing box. Generally, a pre-tightening gap of no less than 5 mm should be left, after which it is necessary to check that the gaps between the valve stem and the packing gland, as well as between the packing gland and the stuffing box, are all consistent. The valve stem also needs to be rotatable; it should operate smoothly, with normal force application and no signs of jamming. If too much force is applied, the packing gland should be relaxed slightly to reduce the grip of the packing on the valve stem ； ⑤V-shaped packing and molded packing rings should be slowly inserted onto the upper end of the valve stem, taking care to prevent the inner ring from being scratched by the threads of the valve stem. The lower packing pad of the V-shaped packing has its protruding corners facing upward, and is placed on the bottom surface ； The concave corners of the intermediate filler point downward, while the convex corners point upward; it is placed in the middle of the filler box ； The recessed corner of the upper packing faces downward, with the flat surface facing upward, and it is placed on the upper layer of the packing box ； ⑥For stuffing boxes with shunt rings, the depth of the stuffing box and the position of the shunt rings should be measured in advance ； The shunt ring must be aligned with the shunt tube opening; a slight upward offset is allowed, but an downward offset is not ； ⑦The O-ring used on the valve stem is an internal O-ring groove ； Those used on the pistons of pneumatic devices are external O-ring grooves, and they all belong to the category of dynamic seals. For the installation of dynamic seal O-rings, special tools should be used in areas that lack mounting chamfers but have threads and grooves ； For O-rings installed by stretching, the sliding surface on the shaft should be smooth and lubricated, allowing the O-ring to slide quickly into the groove. Do not use rolling or manual stretching methods to fit the O-ring into the groove. The O-ring installed in the groove should be free of defects such as twisting, loosening, or scratches; generally, it is necessary to wait for a while after installation so that the expanded O-ring can return to its original shape before the cover can be placed on top. It features an O-ring structure with a retaining ring, which must not be removed during installation. (The compression deformation rate of the O-ring is 16%~30%). ) During the installation of the filler, it is strictly prohibited to use a smaller size in place of a larger one. When the packing width is not appropriate, it is permissible to use packing that is 1–2 mm wider than the width of the packing box groove ； It is not allowed to flatten it with a hammer; instead, it should be evenly compressed using a flat surface or a roller. During installation, the compressing force of the packing should be determined based on factors such as the pressure of the medium and the properties of the packing. Under normal conditions, rubber, polytetrafluoroethylene, and flexible graphite gaskets can be sealed with a lower compression force, while asbestos gaskets require a higher compression force. (The packing compression force should be minimized as much as possible, provided that sealing is maintained.) ) Common problems that arise during the installation of packing include: ① Inadequate cleaning, careless handling, and improper use of tools; that is, the valve stem, gland, and packing box are not cleaned with oil, and there may even be debris inside the box ； Operations are not carried out in sequence; special tools are not used for filling the holes, the filler is cut haphazardly with a chisel, and a screwdriver is used to install the filler, among other issues. ②The filler was selected improperly, using a lower-grade one in place of a higher-grade one, and a narrower one in place of a wider one ； Using ordinary low-pressure packing in high-temperature and highly corrosive media. ③The filler overlaps incorrectly, with varying lengths ； It is installed in the stuffing box in a uneven and imperfect manner. ④Multiple layers are placed and wound together, and compressed all at once; this results in uneven packing within the stuffing box with gaps present. After compression, the outside is tight while the inside remains loose, increasing the risk of leakage from the packing. ⑤Too many packing elements are installed, causing the packing gland to sit above the packing box and resulting in displacement that scratches the valve stem. ⑥The pre-tightening clearance of the packing gland and packing box is too small; if leakage occurs in the packing during use, it becomes impossible to tighten the packing gland any further. ⑦The packing gland compresses the packing too tightly, increasing wear on the valve stem and raising the force required to open and close the valve. ⑧The filler gland is skewed, with uneven tightness. ⑨The gap between the valve stem and the packing gland is too small, causing friction between them and wearing down the valve stem. ⑩Installing O-rings can result in defects such as twisting, scratches, and stretching deformation. 　　The aforementioned problems that often occur with sealing gaskets during installation are mainly caused by the operator’s insufficient awareness of the importance of gasket sealing, as well as a desire for speed, aversion to hassle, and violations of operating procedures. 　　In short, by paying attention to each stage in the design, selection, processing, and installation of packing, and by adhering to the relevant rules and procedures, a range of leakage-related problems associated with packing can be avoided, which in turn helps to reduce valve leakage as well. It is hoped that valve manufacturers will pay proper attention to the design, selection, processing, manufacturing, and installation of sealing packing, in order to prevent any human-induced damage and minimize leaks caused by the packing in valves.

Valve leaks can be either internal or external. External leaks can be resolved by using enclosures or clamps, while internal leaks are more difficult to address due to various underlying causes. However, these issues can generally be avoided by following these steps: 1. Proper valve selection is crucial. The problem of impurities getting stuck, as mentioned by the original poster, falls under this category; gate valves are particularly prone to being blocked by impurities. Therefore, choosing butterfly valves, ball valves, etc., can help solve such problems； 2. The material of the sealing surface: Due to the dishonesty of valve manufacturers these days, there are many valves that suffer from internal leakage; therefore, it is necessary to strengthen the inspection processes upon the arrival of valves at the factory and to reinforce the constraints imposed by contractual agreements ； 3. Operational reasons, especially for high-temperature valves.

1. Pre-installation inspection. 2. Purge and pressure test after installation. 3. Install dual valves to reduce the likelihood of internal leakage.

There are many reasons for internal leakage in valves, mainly including internal factors (wrong selection, poor quality, unreasonable design, substandard sealing materials, etc.) and external factors (severe operating conditions, incorrect operation, scratches during installation, rough or improper handling). If it’s not a real seal damage. Internal leakage can be resolved simply by tightening and adjusting the valve. If it is a genuine seal damage, the best solution is of course to stop the machine, replace the seal or the valve. If it cannot be stopped/ceased, repair must be carried out online while under pressure; there is a certain success rate for such repairs, and even professional teams cannot guarantee 100% success. In companies with advanced technology, once online repair is successful, the valves can be opened and closed freely, and their functional performance returns to its original state. If you want relevant information, please send me a message within the platform so we can all improve together.

It’s often said by those upstairs that it’s just for fun; internal leakage of the valves is an unavoidable problem. So before driving, it’s necessary to perform thorough purging and flushing of the system to remove all impurities. Things like valves on heat transfer oil, similar to steam systems – our company’s valves usually don’t leak under normal conditions. But if they are shut off for a long time before being turned back on, internal leakage can occur and so on. Generally, we just leave it as is or tighten them a bit.

We generally use filters to ensure that the valve is not affected by particles, thereby preventing wear of the valve core.

As everyone upstairs has said, it’s also necessary to perform purging before installation; if the medium contains impurities, then the solution lies in choosing the right type of equipment!