What type of valve is typically found between the boiler and a safety valve?

In a high-pressure boiler system, there is generally no valve located directly between the boiler and the safety valve. Safety valves are designed to be the first line of defense against excess pressure in a boiler. Their primary purpose is to release steam automatically when the pressure exceeds a predetermined limit, thus preventing potential explosions or damage to the boiler.

Having a valve between the boiler and the safety valve would create a risk. If such a valve were to malfunction or become closed while the pressure in the boiler was rising, the safety valve would be unable to perform its critical function of relieving that pressure. Therefore, the safe design practice is to ensure that safety valves are directly connected to the boiler without any intervening valves.

The other options such as pressure control valves, butterfly valves, and check valves are used in various parts of the boiler system, but they do not serve a purpose directly between the boiler and the safety valve. Each of these other valves has specific functions, such as regulating pressure or controlling the flow direction, but they are not appropriate in the context of maintaining a secure pathway for safety relief.