Why do atmospheric gas-fired hot water boilers have to use on-off valves?

There are many valves commonly used in atmospheric gas-fired boilers, including gate valves and stop valves of main steam valves, water supply valves, check valves, exhaust valves, etc.

When the water pump is turned on, the pressure signal is transmitted to the on-off valve of the atmospheric gas-fired boiler through the pressure pipe, the valve is opened, and the water circulation is carried out. When the water pump stops, the pressure drops, and the on-off valve is closed slowly to avoid water hammer, the on-off valve of the atmospheric gas-fired boiler is closed instantly after the circulation pump stops running, blocking the system water flowing back to the gas-fired hot water boiler, and preventing the system water from overflowing from the expansion tank and causing the system water flowing back into the boiler.