Hot Water and Steam Valves
Countries within the European Union have started to ban Glyphosate, the main chemical ingredient in Monsanto’s Roundup, outside of agriculture with some already in effect and others that will become effective in the near future. One particular industry this will affect, is the public gardening services that can no longer rely on Roundup to kill weeds. One effective replacement has been to use hot water and steam to safely maintain garden and lawns. This change to hot water requires new equipment, of which valves are a crucial component to control the on/off function.
News on Roundup’s ban
On March 20th, 2015 the International Agency for Research on Cancer listed Glyphosate as a “probably carcinogenic to humans”. This sparked numerous EU conversations and 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. However, many individual countries within the EU (Netherlands and Belgium to name a few) have banned its use outside of commercial agriculture. This forced private users and public services that relied on Roundup to find a new safe and effective solution.
Replacement solution for Roundup’s ban
Due to this ban, or potential 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, therefore, it will be unable to retain moisture and it will dehydrate. 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/or steam will kill “good” plants as well so it needs to be used with caution.
Types of valves used for hot water and steam
The valves used to control the flow of hot water and steam in these applications are often solenoid valves or electric ball valves, as seen in Figure 1. Most models can be controlled on/off, while special versions feature proportional (modulating) control.
Figure 1: Examples of Electric Ball Valves and Solenoid Valves for Hot Water Applications
Depending on the design of the machine, the valve can have various functions. Often the valve's purpose is to start or stop the flow of hot water to the nozzle. Another function can be to accurately control the flow rate of cold water to the burner to maintain a constant output temperature at the lance. The temperature fluctuation from season to season requires a longer or shorter heating time to reach the desired temperature. These valves should be proportionally controlled.
Solenoid valves and electric ball valves each have pros and cons. Solenoid valves are fast. Usually they are normally closed, which means that they open when energized. Electric ball valves are slower. This can be a disadvantage, but due to the slow speed of opening and closing, it reduces 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. Furthermore, electric ball valves typically don’t use energy to remain in position, while solenoid valves need to be powered to remain in the actuated position. Both valve types can be proportional controlled, making them more complex to specify and operate. Furthermore, they are significantly higher priced.
When selecting a valve, it is important to gather all relevant parameters of the system. Some important steps are:
- What is the circuit function of the valve? Should it be an on/off valve or a modulating valve? 2-way or 3-way valve? Check our article on proportional controlled valves for more information.
- Does the valve need to switch quickly or gradually, does the valve remain open and closed for long periods of time?
- What is the desired flow rate (Kv-value)? Use our Kv calculator to size your valve.
- Determine the maximum pressure and pressure differential. Note that indirect operated solenoid valves require a permanent pressure differential to properly function.
- Determine the temperature of the fluid and the environment. For the housing, either brass or stainless steel materials are used. For the seal, either EPDM or PTFE can be used. For more durability, prevent rust, and a longer lasting valve, manufacturers often choose a stainless steel housing and PTFE sealing.
- Most valves are specified for either 12V or 24V to run on a battery.
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