Figure 1: Steam valves used in a boiler room
Valves designed for steam and hot water are used in several applications across industries like powering turbines, chemical processing, and food. This article discusses the main types of steam valves, the materials used for housing and seal, applications, and the selection criteria while purchasing a valve for steam applications.
Steam is the gaseous state of water. Steam is an excellent working medium in thermodynamic systems and can convey heat across thermal applications after fulfilling its duty as a conducting agent. Read our article on steam hoses to know more about the formation and various types of steam.
Industrial processes typically use steam at lower temperatures and pressures. Hence in a power plant, the steam pipeline requires some form of control to reduce the temperature and pressure of the inlet stream for process application. Steam valves control the pressure level and flow rate of steam and heated water.
Industrial processes use steam at low pressures frequently. Steam has a higher latent heat at lower pressure, increasing energy efficiency. Since the temperature and pressure of steam are mutually related, the temperature is also controlled by controlling steam pressure.
The materials used in the housing and seal of a valve should be compatible with the media flowing through the valve; else, the valve material degrades over time. Metallic materials like cast iron, alloy steel, bronze, copper, steel, stainless steel, and brass are used for the steam valve body and the internal components like the ball and disc. Rubber-based materials like EPDM, NBR, and FKM and plastic-based materials like PTFE and PA are used for the gasket, packing, and seal of the steam valve.
The operating temperature and pressure play a significant role in selecting valve parts from the application. Steam valves are actuated manually or automated and depend on one of the following mechanisms:
The various valve types can have either linear or rotary spindle movement. Rotary type valves are also called quarter-turn valves, and these valves require a rotary motion to open and close. Linear-type valves have a sliding-stem design that pushes an element to open or closed positions. Also, a steam valve can either be a two-port or three-port valve. Two-port valves restrict steam flow through them, whereas three-port valves can add or redirect the steam passing through them.
A ball valve is a quarter-turn operated valve designed to be 100% opened or 100% closed and used to isolate steam in a pipe completely. Steam ball valves are typically controlled with an electric actuator. These valves can be damaged if they are partially opened to control the flow rate; hence, they are better for ON/OFF control and cannot be used to create a pressure drop in steam.
Electric ball valves are slow. This can be a disadvantage, but the slow opening and closing speed reduce the risk of water hammer. A water hammer occurs when a fluid or gas has a quick stop or change in direction. This can damage the valve and other components in the circuit.
Ball valves can handle dusty dry fluids and slurries but cannot be used with abrasive fibrous materials that pose a risk of damage to the surface of these valves.
Figure 2: Ball valve
Butterfly valves are simple and versatile quarter-turn operated valves ensuring quick operation. The valve offers minimum obstruction to steam as it passes through the disc aerodynamically, resulting in minimal pressure drop throughout the valve.
The main advantage of a butterfly valve is the ease with which it can be actuated. The valve can be actuated without requiring high wear and tear or torque. Butterfly valves are also compact, resembling a metal disc, and hence they are easy to be installed. There are no cavities for the deposition of solid particles within the valve body so that these valves can be used for fluids with suspended particles and slurries. Read our article on the comparison between butterfly valves and ball valves for more details on the advantages and disadvantages of each valve.
Figure 3: Butterfly valve
A gate valve is a sliding type of valve where a metal gate slides down to close the valve. Gate valves (also called knife valves) are ideally used as an ON-OFF valve and generally used in the streamline for isolating steam. The valve may be quickly prone to wear and tear due to the vibrations caused in partially open conditions. Gate valves can work comfortably with metal-metal sealing, and these are usually used in high-pressure steam supply lines with superheated temperatures like the lines in the petrochemical industry. These valves are full bore (provides unrestricted flow when the valve is opened) and offer little resistance to steam flow. These valves are cheap and easily repaired but come in big sizes.
Figure 4: Gate valve
A globe valve is a linear motion type valve used in both on-off and throttling applications. A globe valve can be throttled effectively and used to adjust the flow rate of steam. A globe valve comprises a screw-down valve inside a spherical enclosure, and these valves are commonly used in applications where the resistance to steam flow is not a priority. These valves are smaller in size when compared to gate valves and can be throttled more efficiently than gate valves. Poor cleanliness is the most significant disadvantage of a globe valve.
Figure 5: Globe valve
A solenoid valve is electrically controlled and can be designed to be either linear or rotary type. The valve features a solenoid, an electric coil with a movable ferromagnetic core (plunger) in its center. In the rest position, the plunger closes off a small orifice. An electric current through the coil creates a magnetic field. The magnetic field exerts an upwards force on the plunger, opening the orifice. This is the basic principle used to open and close solenoid valves. Solenoid valves are fast. Usually, they are typically closed, which means that they open when energized. These valves need to be powered to remain in the actuated position, and they are costly.
Figure 6: Solenoid valve
A check valve allows the flow of fluid in only one direction. They have two ports, one for media input and the other for media output. These valves are also called non-return valves or one-way valves and are commonly used to prevent backflow into a system. Read our article on check valves to know more about the construction, types, working, and applications of check valves.
Figure 7: Check valve
A pressure release valve is used to control the pressure within a given system to prevent the system from pressure build-up and causing damage to the surrounding equipment. If the system pressure exceeds the valve set point, the valve opens and discharges the excess pressure to the atmosphere or channel it away to a different location. These valves are used in applications where the pressure level is critical such as the petrochemical industry, oil and gas, and steam power generation.
Figure 8: Pressure release valve
Steam valves find extensive use in process control applications. A control valve designed for steam reduces the pressure of inlet steam, thereby controlling steam temperature. Steam valves are generally used for cooling feedwater systems and water, wastewater treatment, food and pharmaceutical industries, fuel handling, and fire protection.
Countries within the European Union have started to ban glyphosate, the main chemical ingredient in Monsanto’s Roundup (currently acquired by Bayer), outside of agriculture, with some already in effect and others that will become effective shortly. One particular industry to be affected is the public gardening services that can no longer rely on Roundup to kill weeds. One adequate replacement has been to use hot water and steam to maintain the garden and lawns safely.
On March 20th, 2015, theInternational Agency for Research on Cancer listed glyphosate as a probable carcinogenic to humans. This sparked numerous conversations in the EU within individual countries. The EU has had discussions regarding banning the substance for agricultural and private use, but on November 27th, 2017, they extended its use until December 15th, 2022. Many individual countries within the EU (Netherlands and Belgium, to name a few) and the US have banned its use outside commercial agriculture. Austria became the first country in the EU to ban glyphosate in 2019, and Germany has decided to go in phases and be completely free of glyphosate by 2023. This forced private users and public services that relied on Roundup to find a new safe and effective solution.
Due to this ban, many companies have turned to hot water and steam as it is cheap, safe, effective, and is a long-term solution for killing weeds. It effectively kills weeds by melting away the coating and severely damaging the plant’s cellular structure, thereby making the plants unable to retain moisture, leading to dehydration. Depending on the water temperature, the plant can die within a few minutes to days. At times, additional treatments may be necessary. Keep in mind that the hot water and steam will kill good plants too, so it needs to be used with caution.
Yes. Ensure you have the correct housing and seal material to withstand the steam application.
You will commonly see solenoid valves and ball valves for steam applications. However, it depends on the application, and the material type is critical.