Basic knowledge of valve maintenance valve installation must pay attention to the matters and details

Basic knowledge of valve maintenance valve installation must pay attention to the matters and details

At present, the technical parameters of the valve produced in the world, the caliber of the door is small to 1 mm to 9750 mm; Valve operating pressures range from ultra-high vacuum 1 x10-10 MMHG to ultra-high pressure 14,600 atmospheres. Valve operating temperatures range from -270℃ to ultra-high temperature 1200℃ and even to 3430℃. Valve medium velocity 11 times supersonic speed; Valve a time to open and close to 1/1000 ~ 5 seconds, the leakage of the valve to 1 x10-10CC/ second, which means the leakage site 300 years later less than 1 CC.

Comprehensive current world production of valve technical parameters, the caliber of the door from small to 1 mm to 9750 mm; Valve operating pressures range from ultra-high vacuum 1 x10-10 MMHG to ultra-high pressure 14,600 atmospheres. Valve operating temperatures range from -270℃ to ultra-high temperature 1200℃ and even to 3430℃. Valve medium velocity 11 times supersonic speed; Valve a time to open and close to 1/1000 ~ 5 seconds, the leakage of the valve to 1 x10-10CC/ second, which means the leakage site 300 years later less than 1 CC. The above examples, through people’s efforts, there will be breakthroughs.

The following are the nominal diameter of the valve, the nominal pressure, the relationship between the working pressure and the working temperature, and the common medium of the valve. Some of the basic parameters have national and ministerial scales.

The nominal diameter of the inlet and outlet passage of the valve is called the nominal diameter of the valve. It is represented by Dg (national standard Dn for trial), in millimeters (mm). The nominal diameter of the valve is specified in the national standard GB1074-70. Nominal diameter series of valves are shown in Table 1-1.

Under normal circumstances, the nominal diameter of the valve is consistent with the actual diameter. There is a phenomenon that the nominal diameter is not consistent with the actual diameter of the cast valve used in high pressure chemical industry and petroleum.

The nominal pressure of the valve is called the nominal pressure of the valve. It is expressed by Pg (the national standard is expressed by PN, the pressure unit is bar), and the unit is kg force /cm2 (kgf/cm2). If Pg16 is marked on the valve, the nominal pressure of the valve is 16 kg force/cm 2. The nominal pressure of the valve is specified in the national standard GB1048-70. Nominal pressure series of valves are shown in Table 1-2. The actual pressure capacity of the valve is often much larger than the nominal pressure of the valve, which is designed to consider the safety factor. In the valve strength pressure test, according to the delimit promised to exceed the nominal pressure, in the working state of the valve, is strictly divided over pressure work, generally choose less than the nominal pressure value.

Three, the relationship between the working pressure of the valve and the working temperature of the valve in the working state of the pressure is called the working pressure of the valve, which is related to the material and the working temperature of the medium of the valve. Denoted by P, the figure in the lower right corner of the P word is the medium relatively high temperature divided by 10 quotient integer. For example, P42 indicates the working pressure of the valve medium at a relatively high temperature of 425℃. Valve working temperature and corresponding maximum working pressure change table referred to as temperature and pressure table. See Table 1-3, 4, 5.

Application example: a 40kg force/cm 2 carbon steel valve in the medium working temperature of 425℃ on the pipeline, its maximum working pressure is how much is the first six out of table 1-3 carbon steel column, find out the working temperature of 425℃ a grid to look down, and then check the nominal pressure column of 40 kg force/cm 2 a grid to look down, The number at the intersection of the two compartments is the large working pressure of this carbon steel valve P4222 kg force/cm 2

The common medium of the valve is a factor to be considered in the design and selection of the valve. How to grasp the “common medium of valve” please read the valve sample and anti-corrosion manual as well as the use and maintenance of valves

Knowledge: Installation of valve must pay attention to the matters and details of the valve installation position, must be easy to operate: even if the installation of temporary problems, but also to control the long-term work of the staff. It is better that the valve handwheel is aligned with the chest (generally 1.2 meters away from the operating floor), so that it is easier to open and close the valve. Ground valve handwheel should be upward, do not tilt, so as not to operate awkwardly. The wall machine depends on the valve of the equipment, but also leave room for the operator to stand. Before installation, the valve should be inspected to check the specification and type and identify whether there is any damage, especially for the valve stem.

The quality of valve installation directly affects the use, so we must really pay attention to it.

(1) Direction and position

Many valves have directional, such as globe valves, throttle valves, reducing valves, check valves, etc., if inverted inverted, it will affect the use effect and life (such as throttle valves), or do not work (such as reducing valves), and even cause danger (such as check valves). General valve, direction mark on the valve body; If not, should be according to the working principle of the valve, accurate identification. The valve chamber of the globe valve is wrong to say that the fluid should be let from bottom to top through the valve port, so that the fluid resistance is small (determined by the shape), open the force saving (due to the medium pressure up), the closed medium does not pressure packing, easy to test, this is why the globe valve can not be inverted. Other valves also have their own characteristics. Valve installation position, must be easy to operate: even if the installation of temporary problems, but also to control the long-term work of the staff. It is better that the valve handwheel is aligned with the chest (generally 1.2 meters away from the operating floor), so that it is easier to open and close the valve. Ground valve handwheel should be upward, do not tilt, so as not to operate awkwardly. The wall machine depends on the valve of the equipment, but also leave room for the operator to stand. To avoid elevation manipulation, especially acid and alkali, toxic media, otherwise it is not safe. Do not flip the gate (i.e. hand wheel down), otherwise the medium will be kept in the bonnet space for a long time, easy erosion of the stem, and for some process requirements contraindicated. At the same time, replacing the filler is extremely unfavorable. Open stem gate valve, do not install underground, otherwise because of wetting and erosion exposed stem. Lift check valve, installation to ensure that the disc vertical, so that flexible lifting. Swing check valves, when installed to ensure that the pin level, so that flexible swing. The reducing valve should be erected on the horizontal pipe, and do not tilt in any direction.

(2) construction homework

Installation and construction must be careful, do not hit the valve made of brittle materials.

Before installation, the valve should be inspected to check the specification and type and identify whether there is any damage, especially for the valve stem. Also roll a few times to see if it is skewed, because in the process of transportation, it is easy to bump crooked valve stem. Also eliminate the debris in the valve. When lifting the valve, the rope should not be tied to the handwheel or stem to avoid damage to these components, should be tied to the flange.

For valves connected to the pipeline, be sure to clean. Compressed air can be used to blow away iron oxide chips, sand, welding slag and other debris. These sundries, not only easily scrape the sealing surface of the valve, among which large particles of sundries (such as welding slag), but also plug the small valve, so that it fails. When installing the screw valve, the sealing packing (hemp and aluminum oil or polytetrafluoroethylene raw material belt) should be wrapped on the pipe thread, do not get into the valve, so as to avoid valve memory product, affecting the smooth flow of the medium.

When installing flanged valves, be careful to tighten the bolts symmetrically and evenly. Valve flange and pipe flange must be parallel, reasonable clearance, so as to avoid excessive pressure and even cracking of the valve. For brittle materials and low strength valves, especially pay attention. The valves to be welded with pipes should be spot-welded first, then the sealing parts should be fully opened, and then welded dead.

(3) Protective measures

Some valves must also have external protection, which is insulation and cooling. Hot steam lines are sometimes added to the insulation. What kind of valve should be insulated or cold, according to production requirements.

In principle, where the medium in the valve to reduce the temperature too much, will affect the production efficiency or frozen valve, you need to keep heat, or even mix heat; Where exposed valves, adverse to production or cause frost and other adverse phenomena, it is necessary to keep cold. Insulation materials are asbestos, slag wool, glass wool, perlite, diatomite, vermiculite, etc.; Cooling materials include cork, perlite, foam, plastic and so on.

(4) Bypass and instrument

Some valves, in addition to the necessary protective measures, also have bypass and instrumentation. A bypass was installed. Convenient for trap inspection. Other valves, also installed by bypass. Whether to install bypass, depends on the valve condition, importance and production requirements.

(5) packing replacement

Inventory valve, some packing is not good, some with the use of media does not match, this needs to change the packing. Valve manufacturers can not consider the use of thousands of units of different media, stuffing box is always filled with ordinary root, but when used, it is necessary to make the filler adapt to the medium.

When replacing the filler, press in round by round. Each ring seam to 45 degrees is appropriate, ring and ring open 180 degrees. The height of the packing should consider the room for the gland to inherit the pressing. At present, the lower part of the gland should be allowed to press the packing chamber to an appropriate depth, which can generally be 10-20% of the total depth of the packing chamber. For high demand valves, the joint Angle is 30 degrees. The seam between the rings is staggered by 120 degrees. In addition to the above fillers, but also according to the details, the use of rubber O-ring (natural rubber resistance below 60 degrees Celsius weak alkali, butadiene rubber resistance below 80 degrees Celsius oil crystals, Fluorine rubber resistance below 150 degrees Celsius a variety of erosion media) three-piece stacked polytetrafluoroethylene ring (resistance below 200 degrees Celsius strong erosion media) nylon bowl ring (resistance below 120 degrees Celsius ammonia, alkali) and other forming filler. A layer of polytetrafluoroethylene raw material tape is wrapped outside the common asbestos disc, which can improve the sealing effect and reduce the electrochemical erosion of the valve stem.

When pressing the seasoning, roll the valve stem at the same time to keep the surrounding average, and prevent too dead, tighten the gland to average force, not tilt.