What is the only valve typically allowed between a boiler and a safety relief valve (SRV)?

The only valve typically allowed between a boiler and a safety relief valve (SRV) is the changeover valve. This valve is designed to redirect flow and ensure proper functioning of the boiler system. In the context of safety, the changeover valve allows for the removal of the SRV for maintenance while ensuring that the system remains operational. It is critical that this specific type of valve be used to maintain the safety protocols required for boiler operations.

Other types of valves, such as isolation valves, check valves, and regulating valves, do not provide the same level of safety assurance. Isolation valves are intended to stop flow, which would defeat the purpose of having an SRV in place, as they can prevent the relief of excess pressure. Check valves are meant to allow flow in one direction and prevent backflow, but they can also pose a risk by inadvertently blocking the outlet of the SRV. Regulating valves, on the other hand, control the pressure and flow rates but can also interfere with the critical function of the SRV by potentially preventing it from opening when needed.

For these reasons, the changeover valve is specifically allowed between the boiler and the SRV to ensure safety and compliance with regulatory standards.