06

2021

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01

How to deal with common problems such as blockage, leakage, vibration, and loud noise of the regulating valve!

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1. The inner wall of the valve body. For regulating valves used in situations with high pressure differences and corrosive media, the inner wall of the valve body is often impacted and corroded by the medium. The pressure resistance and corrosion resistance must be checked with emphasis.

 

1. The inner wall of the valve body. For regulating valves used in situations with high pressure differences and corrosive media, the inner wall of the valve body is often impacted and corroded by the medium. The pressure resistance and corrosion resistance must be checked with emphasis.

2. When the valve seat and control valve are working, due to the penetration of medium, the inner surface of the thread used to fix the valve seat is easily corroded and the valve seat becomes loose. This should be paid attention to during inspection. For valves operating under high pressure differences, you should also check whether the sealing surface of the valve seat is damaged.

3. The valve core is the movable part of the regulating valve when it is working. It is washed away by the medium and corroded most seriously. During maintenance, you must carefully check whether all parts of the valve core are corroded and worn, especially when the valve is under high pressure difference.

The wear of the core is more serious, so attention should be paid (due to cavitation phenomenon). If the valve core is seriously damaged, it should be replaced. In addition, you should also pay attention to whether the valve stem has similar phenomena or is loosely connected to the valve core.

4. Whether the "O" type sealing ring and other gaskets are aged or cracked.

5. Pay attention to whether the polytetrafluoroethylene packing and sealing lubricating grease are aged, and whether the mating surface is damaged. They should be replaced when necessary.

Ways to improve lifespan

 
 

 

Method of extending life by working at wide opening

 

Let the regulating valve work at a larger opening as much as possible from the beginning, such as 90%. In this way, damage such as cavitation and erosion occurs on the head of the valve core.

As the valve core is damaged and the flow rate increases, the corresponding valve will be closed a little further. This will continue to destroy and gradually close, so that the entire valve core can be fully utilized until the root and sealing surface of the valve core are damaged and cannot be used.

At the same time, the throttling gap is large when working at a large opening, and erosion is weakened. This improves the service life by more than 1 to 5 times compared with having the valve work at an intermediate opening or a small opening from the beginning. For example, if a chemical plant adopts this method, the service life of the valve is increased by 2 times.

 

Decrease s, increase working opening and improve lifespan

 

Decreasing S means increasing the losses in the system except for the regulating valve, which reduces the pressure drop distributed to the valve. In order to ensure that the flow passes through the regulating valve, the opening of the regulating valve must be increased. At the same time, the pressure drop on the valve decreases, so that Cavitation and erosion are also reduced.

Specific methods include:

An orifice plate is installed behind the valve to consume pressure drop;

Close the manual valve in series on the pipeline until the regulating valve obtains a more ideal working opening.

It is very simple, convenient and effective to use this method when the valve is initially working with a small opening.

 

Methods to reduce the diameter, increase the working opening and improve the service life

 

By reducing the diameter of the valve, the working opening is increased.

Specific methods include:

Change to a valve with a smaller caliber, such as DN32 to DN25;

The valve body does not change, but the valve core and seat with a smaller seat diameter are replaced.

For example, during the overhaul of a chemical plant, the throttling part dgl0 was replaced with dg8, and the service life was doubled.

 

Method of transferring damage location to improve lifespan

 

Move the seriously damaged area to a secondary position to protect the sealing surface and throttling surface of the valve core and valve seat.

 

Method of increasing throttling channel and improving lifespan

 

The simplest way to increase the throttling channel is to thicken the valve seat to make the valve seat hole longer and form a longer throttling channel.

On the one hand, it can delay the sudden expansion after closed-flow throttling and move the damage position away from the sealing surface; on the other hand, it increases the throttling resistance, reduces the degree of pressure recovery, and makes the steam Eclipse weakens.

Some design the valve seat hole into a stepped or wavy shape, in order to increase resistance and weaken cavitation. This method is often used on high-pressure valves introduced into installations and when old valves are improved, and is also very effective.

 

Changing flow direction to improve lifespan

 

The open flow type flows in the open direction, and cavitation and erosion mainly act on the sealing surface, causing the valve core root and the sealing surface of the valve core and seat to be quickly damaged; the closed flow type flows in the closing direction, and cavitation and erosion affect the sealing surface. After throttling, the sealing surface of the valve seat is below the sealing surface, which protects the sealing surface and the root of the valve core and extends the service life.

When the problem of extending the life of a valve designed to be a flow-open type is more prominent, the life can be extended by 1 to 2 times simply by changing the flow direction.

 

Use special materials to improve lifespan

 

In order to resist cavitation (destruction of shapes such as honeycomb-shaped dots) and erosion (streamlined small grooves), special materials that are resistant to cavitation and erosion can be used to manufacture throttling parts. This special material includes 6YC-1, A4 steel, Stellite, carbide, etc.

To resist corrosion, materials that are more resistant to corrosion and have certain mechanical and physical properties can be used. This material is divided into two categories: non-metallic materials (such as rubber, PTFE, ceramics, etc.) and metallic materials (such as Monel, Hastelloy, etc.).

 

Changing valve structure to improve service life

 

To improve the service life, change the valve structure or select valves with longer life, such as multi-stage valves, anti-cavitation valves, corrosion-resistant valves, etc.

 

Method of reducing stroke to improve diaphragm life

 

For two-position control valves, when the action frequency is very frequent, the diaphragm will quickly break during the up and down folding, and the damage location is often around the periphery of the pallet.

The simplest and most effective way to increase the life of the diaphragm is to reduce the stroke. The reduced stroke value is 1/4dg. For example, the standard stroke of dgl25 valve is 60mm, which can be reduced to 30mm, which is shortened by 50%.

In addition, the following factors can also be considered:

Minimize the membrane chamber pressure while meeting the opening and closing conditions;

Improve the smoothness of the joint between the tray and the diaphragm.