A crown valve — also referred to as a stop valve — is an essential part of an industrial steam boiler system that is used to regulate and slowly dissipate pressurized steam in a boiler. It can also be used to allow the steam to escape the boiler and enter the piping system, providing heat, energy, or other steam functions. These boiler systems are usually too large to be used anywhere but in an industrial plant. The crown valve gets its name from the location the valve is given on the boiler — directly on the top, or the crown, of the boiler unit.
Crown valves are also used as safety measures for boiler systems because they have regulators on them that allow the escape of excess pressure that may build up if too long a period elapses between the valve being opened and closed. The crown valve has indicators that allow the boiler operator to immediately identify whether or not the valve is open. The regulators also ensure that the status of the boiler operation is visible from any vantage point. These types of valves are not considered continuous release valves or controlled release valves, as crown valves are to either be opened fully or tightly closed.
The earliest crown valves were typically manufactured from cast iron, making them very heavy and often times unreliable. The cast iron would bind under heavy pressure, making the valve very difficult to open when pressure had built up behind it. After steel and bronze crown valves became the standard for settings where the boiler units produced higher steam pressures, the introduction of steel and alloy crown valves quickly became the standard among many industrial crown valve manufacturing methods.
When a boiler operator is performing the task of opening or closing a boiler unit’s crown valve, the operator must take note to be cautious and open or close the valve slowly and deliberately. Not doing so can cause something called waterhammering, which occurs when a high amount of steam pressure is released from the boiler too quickly and “hits” the junctions in the piping system. If the boiler unit is closed by the crown valve too quickly, a sudden increase in boiler pressure can occur, which can damage the fittings in the boiler system. Most often, a secondary valve is fitted into many high-pressure systems to avoid either of these circumstances.