DFT® specializes in manufacturing check valves designed for a wide range of applications, including those that require handling severe service conditions. Typically, when engineers think of severe service, they think of high temperatures and/or high pressures. However, severe service applications also include high cycling applications. They are going to explore two high cycling applications, including the challenges and DFT®’s severe service valve solutions.

Digester Service

The paper pulp digester serves as the key equipment in the production process of chemical pulp. It is used to cook raw materials for papermaking (e.g., wood, grass, bamboo, and others) to produce pulp mainly containing cellulose by chemical interaction with the cooking liquor.

This process includes steam injection at up to 150 PSIG. The steam is pulsed into the digester several times per hour. While 150 PSIG is not considered severe, the constant pulsing can take a toll on equipment.

Digester Solutions

Several end users have experienced premature failure of traditional swing-type check valves in this application. When the swing check valves fail, the black liquor used to break down the pulp and the pulp itself would migrate upstream past the failed swing check and damage upstream piping and equipment.

The end users reached out to DFT® to develop an Axial Flow Non-Slam Check Valve solution to this problem. DFT® developed several styles of severe service check valves with special construction to handle this high cycling application. The DFT® solutions include the GLC® SS short-pattern flanged check valve, the Excalibur® SS a B16.10 long-pattern flanged check valve, and the WLC® SS wafer-style check valve.

All of these check valve styles have upgraded internal materials selected to withstand constant high cycling. The upgraded materials include 17-4 trim with a Xylan-coated one-piece welded disc stem assembly, 17-4 bushings, and an X-750 spring.

Compared to only getting several months of service life with the swing check valves, end users now get extended years of service life with the DFT® Axial Flow Non-Slam Digester Severe Service Valve solution.

Boiler Feedwater Service

All power plants—including natural gas-fired, coal-fired, and nuclear power plants—have boilers. The boilers generate steam to power turbines that generate electricity. Water must be heated in boilers to generate steam. The water is delivered to the boilers by boiler feedwater pumps.

Boiler feedwater is typically in the range of 180 °F to 225 °F. These temperatures would not be considered severe. However, depending on the design of the system in power plants, the temperature may be even higher, often 300°F to 350°F , especially if feed water is preheated by economizers or heaters using steam from the turbine or other heat recovery processes. Feedwater pump discharge pressures can vary between 700 and 1400 psi depending on boiler demand.

Check valves are installed between the outlet of the boiler feedwater pumps and the inlet of the boilers and/or deaerators. The check valves are installed to prevent backflow out of the boiler that can damage expensive feedwater pumps and other upstream equipment. Not only is this a high-cycling operation, but it is also a high-pressure application with varying pressures depending on boiler load. This is a very demanding application. As with the digester application, traditional swing checks typically experience a high failure rate in this application.

Boiler Feedwater Solutions

DFT® developed the WLC® BF specifically for boiler feedwater applications. The WLC® BF has upgraded hardened materials selected to withstand high pressure, pressure swings, and high cycling. The upgraded materials include a WL9 body, a 4 ribbed body construction, greater wall thickness, 410 trim, a one-piece welded disc stem assembly with Colmonoy-coated stem, carburized bushings, and an X-750 spring.

Compared to only getting several months of service life with the swing check valves, end users now get extended years of service life with the DFT® Axial Flow Non-Slam Boiler Feedwater Severe Service Valve solution.

Valve Types

DFT® offers the following valve types for digester, boiler feedwater, and other severe service applications. These valves are constructed from high-quality, heavy-duty materials with tight seals to withstand the harsh operating conditions of their application:

• DFT® Model WLC® BF (Boiler Feed): The DFT® Model WLC® BF wafer style check valve is for severe duty boiler feed service applications and other severe duty applications.
• DFT® Model GLC® SS: The DFT® Model GLC® SS is a severe service short-patterned flanged silent check valve designed for digester applications and other severe service applications.
• DFT® Model WLC® SS: The DFT® Model WLC® SS is a severe service wafer style check valve for digester applications and other severe service applications.
• DFT® Excalibur SS: The DFT® Excalibur SS is a severe service flanged silent check valve for digester applications and other severe service applications. This valve is B16.10 and a direct replacement for a swing check valve.

Severe Service Check Valves by DFT® Inc.

Severe service applications require specialized valve solutions. DFT® Inc. offers an extensive product line of robust severe service silent check valves specifically designed for these high-pressure and high-temperature environments. They are certified by ISO 9001:2015 and many other valve standards such as 3-A Sanitary Standards, Manufacturers Standardization Society (MSS), American Petroleum Institute (API) SPEC 6D, and European Pressure Equipment Directive (PED) to provide quality, long-lasting valves you can depend on.