High-pressure water valve selection & maintenance, Part 1

Diagram of a poppet valve

Pick the appropriate valve design & configuration

Once the operating parameters are defined, the engineer should specify the high-pressure water valves needed to meet the operation and actuation requirements of the application. The following are the most common high-pressure water valve designs for hydraulic applications:

• Poppet valve — A cone- or ball-shaped plug is held in place on the valve seat by a bias spring or hydraulic piston when operating as normally closed. When the plug is permitted to move away from the valve seat, fluid flows through the valve. This industrial valve offers a higher flow rate than spool-style valves. Its internal seals experience less wear, extending its operational life.
• Spool valve — This industrial valve contains a piston or spool that extends and retracts in the valve housing. As the spool travels, it opens or closes ports in the valve body. Flow through the valve is determined by the position of the spool. Spool valves are not affected by pressure, requiring less force for actuation. They are balanced and can be used for vacuum operation.
• Hollow bore spool valve — With this type of industrial valve, the spool is hollow and contains a series of slots spaced evenly around the circumference of the spool. This valve can operate over extended periods of time with water that contains some degree of contamination from sand or scale.

Poppet and spool valves can be configured for many high-pressure applications:

• Isolation — When configured as a two-way isolation valve, the valve will have two ports: an inlet and an outlet. The purpose of the isolation valve is to allow or shut off flow.
• Directional control — These valves are used to extend and retract hydraulic cylinders such as those typically used in a forging press.
• Pump bypass — In most high-pressure water hydraulic systems, the pump needs to run continually. Pump bypass valves are ported to direct water back to the flume or reservoir to recirculate through the pump when there is no system demand so the pump does not overheat.
• Check — Check valves prevent flow back into the circuit caused by multiple pump sources of pressure. Flow can only occur in one direction through a check valve.
• Prefill — Used to reduce water hammer and damage to the upper header nozzles, prefill valves allow the filling of a system header with low pressure water from an external low-pressure source or with system pressure when used in conjunction with a pressure breakdown orifice.
• Safety — Safety valves are typically poppet-style and are installed in circuits to prevent system overpressure. When the valve detects a pressure greater than the set limit, flow is directed to a relief port.

Remember, the industrial valve selection process should begin during the system design phase. In addition to choosing the best valve design and configuration, the engineer also needs to consider the available valve materials.

Choose the proper materials of construction

Materials of construction have long-term impacts on the performance of the industrial valve and the overall hydraulic system. When choosing high-pressure water valve materials, the following factors should be considered:

Hollow bore spool valve diagram showing the location of materials used for valve body and packing.

Common materials for valve bodies, seats & spools

When selecting industrial valve materials, consider the corrosion level, temperature and pressure of the application. Also, certain materials are less susceptible to wear. Some characteristics of popular materials for valve bodies, seats and spools are:

• Ductile iron — Low in cost, readily available, easily absorbs shock, poor corrosion resistance
• Brass and bronze — Low in cost, readily available, improved corrosion resistance over ductile iron
• 316 stainless steel — Excellent corrosion resistance, high tensile strength at elevated temperatures, costlier than cast iron, brass and bronze valves
• Monel (nickel-copper alloy) — Superior corrosion resistance, ideal for cladding of valve trim parts
• Inconel (alloy of nickel, chromium and iron) — Ideal for handling corrosive media, maintains strength at high temperatures

Popular materials for valve seals, gaskets & packing

Consider the following characteristics of popular materials of construction for various valve components:

• Polyurethane — Highly durable, designed for temperatures up to 200°F, ideal for pressures up to 6,000 psi, excellent abrasion resistance
• Viton — Excellent chemical resistance, works well at high temperatures
• Polytetrafluoroethylene (PTFE) — Extremely low friction, designed for a wide range of pressures and temperatures
• Glass-filled PTFE — Improved creep resistance, improved wear resistance and heat transfer
• Polyetheretherketone — Ideal for steam applications, high temperature rating, good corrosion resistance

After selecting the optimal valve and materials of construction, steps should be taken to minimize leakage and ensure the reliable performance of the high-pressure hydraulic system. Stay tuned for Part 2 in this article series, which will discuss best practices for managing industrial valve leakage and preventive maintenance.