All rod drive control valves require some kind of seal that allows the rod to move from certain external devices (actuators). While sealing the process fluid so that there is no leakage between the moving rod and the body. Valve Packing Material are generally from sealing mechanism is packaging.
These mechanical properties do not differ from the filling boxes used to seal seawater. On the ship or when the ship penetrates through the hull of the propeller shaft:
The fundamental problem for a ship is the same as the control valve. How to allow a moving shaft to pass through certain fluids requires an impenetrable barrier.
The solution is to wrap the shaft in a flexible material, maintaining a tight fit. With the shaft without tying the movement of the shaft.
The traditional packaging material used for boat propeller shafts is the linen rope. The material does not cause excessive friction to the movement of the shaft.
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PTFE Valve Stem Packing
Modern marine filling boxes use advanced materials such as Teflon (PTFE) or graphite instead of flax, which wear more and lose less water.
In the world of control valves, the traditional packaging material used to be asbestos. Just like the linen material used to fill boxes), but now it is often PTFE or graphite as well.
A small leak isn’t problem for the filling box of a boat, since all boats equipped with bilge pumps that pump the collected water over time.
An absolutely unacceptable in many industrial control valve applications where fugitive emissions must minimized.
“Exhaust discharge” means any unwanted escape of process substances entering the surrounding environment, usually from leaks around pumps and valves.
The special “environment” kit used in control valve applications and considered.
The sliding rod valve packaged for the part of the body called a bell. So the simplified figure of the single-hole rod guided ball valve shows:
Here, the packing material is in the form of multiple concentric rings, stacked on the valve rod as a washer on a bolt.
These packing rings forced down from above by the packing flange to apply compression force around the valve rod.
This compression force necessary to create mechanical stress on the packaging material. So well sealed with the valve rods and the inner walls of the hood.
The two nuts threaded to the bolt maintain proper force on the packing ring.
This friction not only prevents the precise movement of the valve stem, but also causes improper wear on the stem and packaging, increasing the likelihood of future packaging leaks.
Improper force of the packaging flange can result in poor sealing and process liquid can exit the valve through the packaging.
A closer look at the hood reveals that many components work together to form an airtight, low-friction seal for moving valve rods:
In this picture, we see two sets of packing rings separated by a piece of metal called a lantern ring. The flashlight ring acts as a partition, allowing the lubricant introduced through the lubrication port to enter the two packing kits from the center of the hood.
The packaging shown here “loaded” by the compression force applied by the packaging followers.
- The only elasticity of this special system lies in the packaging material itself.
- A fixed load, also known as jam wrap.
- Over time, with wear and fatigue of the packaging material, packaging followers should re-compress by carefully tightening the packing nuts.
Take care when turning the packing nuts into a gently loaded package. Insufficient torque (resulting in insufficient effort applied to the packaging) lead to leakage of process fluid.
Excessive torque (which causes excessive stress on the packaging) can lead to friction of the rod and premature packaging failures.
The latter situation is often found in an industrial environment where well-intentioned but knowledgeable personnel squeeze the valve packaging too much to prevent leakage.
If the packaging component continues to drip after the right pair, the right remedy is to replace it and not tighten it further.
Another way to “fix” the load is to insert the metal spring into the packaging assembly, so that the spring elasticity helps maintain the proper packing tension as the packaging material wears and ages.
This is called live loading, examples of which look like this:
In an example, we see coil springs inside the hood for live fillers.
In another example, we see a set of spring steel washers called Belleville springs.
Belleville springs have a concave profile that allows them to withstand compression along the shaft.
These spring washers are always stacked in opposite positions (bump to concave, convex to convex), so the washers have compression space.
The actual valve packaging assemblies are removed from the hood (left) and remounted to the rod (right), showing the packaging structure and related components.
This package does not have a flashlight ring, but has a helical spring.
This makes it a living wrapper, not a jam wrapper.
In packaging applications where external lubrication is required, the rod packing lubricator can be connected to the bonnet lubrication port.
The unit uses a long threaded bolt as a piston to introduce a certain amount of grease into the packaging assembly:
How to Operate After Installation
To operate the lubricator, first fix the manual valve on the lubricator in a closed (closed) position. Then completely unscrew the screw until it exits the lubricator body.
Proper grease is tightened into the bolt hole of the lubricating body and the bolt is screwed back into place until the hand is tightened.
Use a wrench or wrench to tighten the screw further (creating pressure on the grease). And open the manual valve to allow grease to enter the packing chamber.
Then the bolt is tightened completely, pushing all the amount of grease into the package.
The manual valve is completely closed, so the process liquid can not leak through the bolt thread.
The two most common packaging materials currently used are Teflon (PTFE) and graphite.
Teflon is the best in fluid sealing, rod friction and rod wear.
Teflon is also quite resistant to various chemical attacks. Unfortunately, its temperature range is limited and can not withstand strong nuclear radiation.
Graphite is another self-lubricating packaging material with a much higher temperature range. Teflon and its ability to withstand hard nuclear radiation and Bitflon produces more dry friction.
Due to the electrical conductivity of graphite fillers. They also have the unfortunate electrical corrosion properties between the rod and the metal of the hood.
Sacrifice zinc washers are sometimes added to graphic packaging assemblies to help mitigate this corrosion. But this will only delay, not prevent, corrosive damage to the rod.
The photo below shows samples of “rope” bundles of woven graphite (left) and PTFE (right). Where it is often found that longer portions bend around the valve rod to form a seal.
The graphite filler has a glossy surface and easily scales, while the Teflon filler is pure and maintains its integrity.
In order to combine the best properties of the two materials, mixed packaging materials such as carbon-reinforced PTFE have been developed.
Traditional valve packaging material is asbestos, which is woven into packaging rings in the same way as graphite fibers woven into modern packaging rings.
Asbestos is a suitable mineral for high temperature process applications.
Its non-conductivity eliminates the problems inherent in electrical corrosion of graphite.
Unfortunately, its classification as a hazardous substance excludes its use as packaging material for contemporary applications.