Gland Packing: The Definitive Guide

virgin PTFE packing

The Gland Packing is a sealing element used for shaft sealing to solve dynamic sealing constructions. In rotary motion, the gland packing is important for the efficiency of pumps, mixers, valves, and other industrial equipment. It is a rope-like construction usually braided with synthetic fibers like acrylic, nylon, polyester, latex, and Kevlar saturated with grease or impregnated with graphite or PTFE.

Sometimes metal wires will be added to strengthen the packing and make it better in anti-friction properties.

Gland packing Features:

Always the gland packing has the characteristics of anti-friction feature which will make the gland packing provide better sealing function when the shaft moves which will generate heat and friction occurs.

No chemical reaction makes the braided gland packing not collapse when seals the liquids.

Temperature resistance is to ensure the braided packing suitable for the working environment.

Resilience and comprehensibility: The gland packing will compress when it is working and receive the pressure from the flange, and then it will strengthen the shaft and return back to its original shape on the release of the tension. In this way, the gland packing will give a good sealability.

No contamination with the fluid: The gland packing should not contaminate the fluid when in some industries especially pharmaceutical and the food industry.

Non-corrosive: The gland packing should be not corroded in working conditions to prevent any damage to the shaft.

Lubricant retention: The lubricants like grease, graphite maintained with a gland packing will provide it better anti-friction properties.

 

Applications for Gland Packing:

Gland packings are used for sealing in below applications:

  • To seal in static applications like manholes, tank hatchet.
  • To reduce leakage along the stem in gate valve, ball valve and globe valves.
  • To reduce leakage of the working fluid in reciprocating pumps or rotating pumps like centrifugal pumps and screw and gear pumps.
  • To seal propeller shafts in lifeboats and merchants ships of older generation.

The above applications requires different gland packing material, Then it goes to the selection of gland packings. It is very important as an incorrect choice will lead to failing in service and leakage.

 

Selection of Gland Packing:

The gland packing is aim to seal the gap on the rotating shaft by controlling the leakage of the medium and reducing the unnecessary emission into the environment. We have four main criteria to choose the correct packing:

Operating Temperature: There should be a safe margin of the max. working temperature for the gland packing especially in the case of dynamic application. As most material’s temperature exceeds when during operation, the friction occurs and the temperature will increase accordingly which will result in overheating and burnout of machine parts. Then we can also see that the medium temperature is not the same as the packing temperature, due to the friction, gland packing works at a higher temperature. For these occasions, graphite and carbon fiber-based gland packing is a good solution. From the above description, we know it’s critical to select a proper temperature range to avoid immediate failure or leakage.

Sealing Pressure: When the gland packing is installed into the stuffing box, it is tightened and compressed between the shaft and stuffing box wall. When compressed, the packing will expand and exert a radial force against the shaft. Then friction is generated and the gland pressure is regulated to provide lubrication to seal and prevent overheating.

Shaft Speed: When a gland packing is working, the movement between the shaft and the packing will generate friction which will result in wear of the packing and the generated heat will degrade the packing’s properties. Most pumps and equipment are specified with the shaft speed to tell us the number of revolutions per minute. It is very important to know the working condition of the gland packing.

Chemical resistance: To ensure the packing won’t be corroded in the sealed fluids is crucial as corroded material will degrade gland packing’s function and lead to leakage. It is good way to choose material with full PH range of 0~14.

 

Except above main factors, we also need consider the gland packing’s material. As braided packing is always made of the combination of the materials and a really wide range of material can be selected.

Materials for Gland Packings:

Of a great variety of gland material in the market, we always classify them into five basic kinds:

Natural fibers, flexible graphite, PTFE, Aramid and carbon fibers. These are the most common and important combination of the braided packings. These five kinds of material have their own characteristics and are not interchangeable or replaceable for specific working conditions.

Always the gland packing will be impregnated to improve its sliding properties and heat dissipation and anti-friction. The most common lubricants / impregnates are graphite, PTFE dispersion and grease.

Natural fibers: it refers to cotton, ramie which is natural planted. The most common packing our clients get from us is ramie packing with PTFE impregnation. This packing has excellent mechanical characteristics and resistance to abrasive wear and low friction. It is good option for hygienic applications but not suitable for wide range of working temperature and easily be influenced by chemical factors. The max. working temperature is 120℃ with PH 5~9 and linear velocity is 6m/s.

Application for natural fibers packing is clean water and brine where temperature is limited and with no strong chemicals.

Flexible Graphite: It’s made into graphite yarn from flake graphite which has good thermal and chemical resistance, thermal conductivity and self-lubricating properties. Then braid the yarn to packing structure. And it’s also flexible. It is perfect packing for environment with heat shocks and overheating. The graphite provides a really good anti-friction feature and sliding characteristics. The max. operating temperature is 450℃ with PH 0-14 and linear velocity is 40m/s.

Application for graphite gland packing is dynamic centrifugal pumps for water, petroleum derivatives and other chemicals, especially under high speed and high-pressured and temperature conditions.

PTFE: With excellent chemical stability (withstand strong oxidants, ozone and acid, alkali), corrosion resistance, high lubricity, non-sticky characteristics, aging resistance and long-term service in wide range of temperature (-180℃~+250℃), low coefficient of friction, PTFE Packing offers a wide range of use in most industries.

There’re two types of PTFE-based packing: 100% pure PTFE packing (white PTFE Packing) and Graphite PTFE Packing (black PTFE packing). Pure PTFE packing is supposed to be used in hygienic applications and food industry while graphite PTFE packing is suitable for higher range of shaft pressure and speed as it has better sliding performance and heat resistance.

Apart from above two types of PTFE Packing, we also have other PTFE combined with aramid fiber packing: PTFE Packing with aramid corners, Graphite PTFE packing with aramid corners, Graphite PTFE Zebra patterned packing. These packings are braided with white / black PTFE and aramid fiber, by adding aramid fiber and graphite impregnates, the packings provide better abrasive resistance and sliding properties. They are suitable for dynamic sealing conditions with a higher linear speed and pressure. These hybrid packings composed of aramid and PTFE are used in chemical industry, oil and gas, pharmacy, electricity and equipment of centrifugal reciprocating pumps, agitators and mixers, etc.

The max. working temperature for PTFE Packing is 260℃ with PH 0~14 and linear velocity of 15m/s while 25m/s for graphite PTFE packing.

Aramid Fiber: It is a synthetic fiber with good strength and abrasion resistance, high resilience and low cold flow. It is also called artificial metallic wire due to its strength, so it easily wipes the shaft. That’s the reason we always impregnate it with PTFE or graphite emulsion and lubricants to provide a high efficiency and durability in dynamic seals.

Besides above combination packing (Aramid and PTFE), there’re aramid fiber packing which is braided with aramid /Kevlar fiber impregnated with PTFE emulsion and it provides very excellent resistance features and Aramid Spun yarn Packing which is made with discontinuous twisted yarn. The spun yarn packing is braided with each impregnated aramid yarn and then impregnate again on the packing body during the braiding.

The packings can resist more severe media and higher pressure, it is ideal end rings with other packing rings to protect entire set of packing rings from abrasive particles by reducing friction to improve service life.

The max. operating temperature is 260℃ with PH 3~12 and linear velocity is 10m/s.

Carbon fibers: It is light and durable and resistant to high temperature and abrasion. It’s a new material with excellent mechanical properties, no creep, good corrosion resistance and thermal conductivity. Carbon fiber packing is suitable seal for dynamic seal application due to its high thermal conductivity. It can instantly conduct the heat generated during the movement of the sealing material and shaft, in this way the seal environment won’t be overheated and the equipment work properly. Its low coefficient of thermal expansion makes it suitable in dynamic seal of severe conditions. The lower the coefficient of friction, the less power consumes. Which enable the carbon fiber packing be suitable for high speed dynamic seal application and longer working life due to its low abrasive resistance and high strength.

The max. working temperature is 600℃ with PH 0~14 and linear velocity is 20m/s.

Above are the basic material for braiding the gland packings, usually we can also add stainless wire like Inconel wire and silicon rubber core to provide the packings with high strength.

 

The most commonly used gland packings:

Despite there’re so many different materials for gland packing and different combination of the material, we can provide almost 20~30 different types of gland packing, but the most commonly used are only several types as below:

Graphite Gland Packing: It is made of pure flexible graphite yarn and it has the advantage of good self-lubricity and heat conduction, small friction coefficient, high strength and good softness which can protect the valve’s stem while under operation.

Sometimes we can add fiberglass and stainless wire or Inconel wire to strengthen the pure graphite packing and enable the packing shoulder higher pressure and higher temperature and provide a longer working life.

PTFE Gland Packing: It is braided with 100% pure PTFE yarn with on other addition to it. So it’s widely used in pumps and valves which request clean and no contamination. It is FDA approved and can be used in food and pharmacy industries.

There’s another PTFE packing which is made of stretched PTFE yarn fully impregnated with PTFE latex. It has better performance in react to pressure and a smaller friction coefficient compared with pure PTFE packing.

Graphite PTFE Packing: It is packing made of PTFE yarn impregnated with graphite emulsion. The gland packing combines the characteristics of PTFE and graphite together to make it a good packing with low friction, flexibility, heat conduction and resistance in most desirable ranges. It is suitable for dynamic sealing conditions with media flow of high linear velocity.

Aramid Gland Packing: It is braided with aramid / Kevlar fiber impregnated with PTFE and lubricating oil. It provides good resistance to chemicals, high tensile strength, low cold flow and can be used in conditions with high rotating speed.

And there’re several types of hybrid aramid packing, such as graphited PTFE packing with aramid corners, Pure PTFE packing with aramid corners, graphited PTFE packing with aramid in zebra format. These packings improve sliding properties, flexibility and heat dissipation.

Ramie PTFE Packing: It’s braided with natural ramie yarn with impregnation of PTFE and impregnate in PTFE emulsion while weaving the packing. It has good sealability, lubricating.

The packing ensures tightness under lower pressures of the gland.

 

How does Gland packing work?

A gland packing works as a mechanical seal but with lower cost, it is soft and flexible to be inserted into the stuffing box (a gap between the shaft and the pump housing)/ packed around the shaft. The gland packing will be compressed to form a seal to prevent any leakage of the medium when the tap of the pump is turned on. And the gland packing’s characteristics which we just mentioned above will enable the packings for longer working life and require little maintenance.

 

How to install the gland packing:

It’s important to install the gland packing correctly to avoid of any failures during operation.

Below are the procedures for the gland packings’ installation:

  • Lockdown and close valves and relieve all pressure.
  • Remove all the old gland packings from the stuffing box. Clean the stuffing box and check if it’s worn or not. Replace it if it’s worn a lot.
  • Choose the right dimension of the gland packing or die-formed packing rings.
  • When using coil or spiral packing, remember to cut the packings into separate rings. Do not wind, cut on the mandrel the same size as the sleeve. Hold the packing rope tightly around the mandrel and remember do not stretch it. Cut the rings and make sure it fits the packing space properly.
  • Install one ring at a time. Sometimes lubricant is required inside of the stuffing box.
  • Install the right numbers of the rings or correct length of the rope packings.
  • After finishing all the rings’ installation, take up bolts finger tight or slightly snugged up.
  • There should be an allowance for leakage freely at first and gradually tighten the gland to a certain leakage rate, which will result in a better packing job for a longer period of time.

But do not over tighten.

  • Replace the packing if uncontrolled excessive leakage occurs.

Where can I buy the gland packings and how can I place gland packing orders:

We Ginseal has more than 30 years of sealing experience, we can provide a wide range of selection of gland packings.

Above mentioned packing types are all in our range, you can kindly contact our sales to get a high-quality braided gland packing at a competitive price. Our products are sold to Europe, the North of America and the South of America, Southeast Asia, the Middle East, etc.

If you are not sure about what kind of gland packing you need, we can provide our professional suggestions based on the application.

When you make an inquiry or an order, please just let us know the dimensions/cross-section of the gland packing and the material.

Dimensions / Cross-Section we usually supply: 1/8” ~3” (3x3mm ~75x75mm)

Regular Package: 2.5 kgs/roll, 5kgs/roll, 10kgs/ roll, etc.

Special dimensions or packages are also available upon request.

 

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