by Denise Sullivan Denise Sullivan No Comments

5 Common reasons of Valve Seat Failure

valve seat failure

 

Valve seat failure can lead to costly and time-consuming issues. Under certain circumstances, a ball valve seat failure can cause explosions and lead to life-threatening situations. In this article, we will cover the top five causes of failure.

Material Choice

The material choice of the valve seat can contribute to valve seat problems if you pick the wrong option. Different materials work in different operating conditions, so you want to ensure that you research the material carefully before choosing.

The most common material options are 

  • PEEK
  • PTFE
  • TFM
  • PCTFE
  • Acetal
  • Vespel

The wrong material can cause unexpected issues that may damage the hardware of mating components or even physical injury.

Cold Flow

While PTFE, or Teflon, is a common material in valve seats, there could be some cold flow resistance issues. Cold flow is the process when solid material slowly deforms under the influence of long-term mechanical stress.

The cold flow of material during us and cycling causes a slow deterioration in valve performance. Despite cold flow issues, PTFE is still the best choice in many industries. Choose a filled PTFE instead of virgin PTFE to mitigate complications from cold flow. Filled is less susceptible to stress and has better resistance to cold flow.

Excessive Friction

Excessive friction can also cause valve seat issues. Excessive circumferential seal force accelerates wear on the valve, which leads to an increase in torque requirements. The friction between the ball and the valve seat affects how much torque is necessary to turn the ball valve. 

 When the temperature in the valve increases, the pressure between the valve seat and the ball increases. Increased temperature creates greater friction between the valve ball and the seat. 

Eventually, the valve can become locked either open or closed. As the required torque increases, the valve seat is torn apart, and mechanical failure occurs.

Valve Seat Failure: Seat and Seat Carrier Design

The valve seat is one of the most critical components. However, poor seat design can lead to a shortened lifespan, leakage, or catastrophic failure. The catastrophic failure could lead to explosions or life-threatening damage in particular environments.

Soft seat valves typically use metallic seat carriers with the valve seats pressed into them. As with the seat design, the seat carrier design can have similar problems. If the seat carrier design is slightly off, it could make it difficult to determine where the problem lies.

Permanent Deformation

In high-pressure applications, the valve setting of soft seats is necessary. To correctly set soft seals, the valve is repeatedly actuated during part of the build process. This repeated actuation can cause permanent deformation during normal use.

A failure to understand the initial deformation will cause the valve to fail. It won’t fail on initial use, but it will eventually stop working, and the valve will either need to be rebuilt or replaced as a result.

Valve Seat Failure Conclusion

Whether your valve requires PTFE, PEEK, or any other material, you want to ensure you get the appropriate material for your valve seat. Incorrect materials and excessive friction, seat design malfunctions, and permanent deformations can cause failures. 

Contact us today to learn more about the valve seats we offer and assist you in finding the appropriate material for your applications.

 

by Denise Sullivan Denise Sullivan No Comments

Molded PTFE Billets: An Overview

Molded PTFE Billet

Teflon (PTFE) billets are compression molded tubes and rods made of Polytetrafluorethylene used in numerous industrial applications covering almost every industry, including chemical processing, automotive, food, aerospace,  medical device, semiconductor, and fluid handling. These functional parts are popular due to Teflon’s chemical resistance, extreme temperatures, low friction properties, and ability to mold them into the precise shape and size needed.

Types of Molded  PTFE Billets

The molded processing techniques we employ are compression, isostatic, and automatic. The determination of which method to use will depend on the type and size of billets being produced, the industry they are being used in, and the manufacturer’s preference.  

Compression

Compression molding for PTFE  billets is one of the three main processes, with isostatic and automatic as the other options (we will discuss these in a later article). To make a billet using this process, one must design and create the source mold for the rod or tube. The compression mold is a two-part mold that includes a preform component.

The performance has the same shape as the tube or rod being processed.  The material is loaded into the mold, pressed under specific pressure and time depending on the grade of PTFE being processed, and then ejected for the mold. 

The pressure causes the material inside the preform to conform to the mold’s shape. As a result, any excess material leaks out of the mold. Once the molding process is complete, the billet is ejected from the mold.

Once the billet is extracted from the mold, it is now in what is called the “Green State,” compact into the desired shape, but no molecular change has occurred; this only happens after sintering in our ovens for a designated time between 650 to 715 degrees F. 

The billet is left to cool at room temperature. Once cooled, excess material can be machined off to make a smooth, perfectly formed Teflon billet. 

Advantages of using compression molding include:

  • Strong parts
  • Lower tooling costs
  • Broad design options
  • Lower waste generation
  • Large part manufacturing

Sintering Molded Tubes, Rods, or Semi-Finished Parts.

Sintering results in a change in the PTFE powder that reorganizes the molecules into a compound. To sinter Teflon billets:

PTFE Powder

 

  • Temperatures must be between 675°F and 700 °F (357°C and 371°C).
  • The oven must have good airflow.

  • Billets must be supported to ensure that they do not sag

Adding an annealing cycle during the sintering processes will help to stop cracks from forming while the compound bakes. Once the billets are out of the oven and cooled to room temperature, they can be machined.

Molding Process

While all molds have physical property variations, the overall process is similar. Therefore, the variations between compression, isostatic, and automatic molded billets are inconsequential to the prevalent use. 

The molding process is two-step. It begins with packing the mold and pressing the powder,  called the “green state.” Next, the mold is placed under specified pressures depending on whether the material is unfilled (Virgin) or filled with various fillers, glass, carbon, graphite, etc. pressure of up to i.

After pressing, the item is removed from the mold. Workers must be careful during the ejecting of the tube or rod. Mishandling of the green material could result in cracks. Once the mold is removed, the billet is sintered.

conclusion

Molded PTFE billets are ideal for many industries. The properties of PTFE make them chemical resistant, have a low coefficient of friction, and can be manufactured compliant with FDA, Class VI Medical, NACE, Aerospace, and Semiconductor  Standards approved for use in medical and food industries. In addition, clean Room Molding for Ultra Pure applications is available.