The orifice diameter is the internal opening of the valve and is used to calculate the flow capacity of the valve. Metric or English makes no difference. It’s the inside hole. The inlet size is the interface or the size/type of the threads where you attach the valve. As of publication Kingston Valves do not come in metric sizes, only NPT (National Pipe Thread).
Typically, the valve should be nameplate set to open at the MAWP (Maximum Allowable Working Pressure) of the vessel the valve is intended to protect. There is a tolerance to actual set pressure, which means a valve set at 100 psig nameplate may open slightly above or below 100 psig. Consult the current ASME Boiler and Pressure Vessel Code for tolerance classes and special situations when the set pressure may be different than the MAWP.
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It is normal for spring-operated safety valves to exhibit leakage or simmer/warn, as the operating pressure approaches the nameplate set pressure, typically in the 80%-90% range of nameplate set pressure. The ASME Boiler and Pressure Vessel Code does not require a specific seat tightness requirement. A certain level of leakage is allowed per manufacturers’ published literature. Kingston defines seat tightness standards as follows: Factory Standard Seat Tightness Performance: o Hard Seat Valves – no audible leakage at 20% below nameplate set.
Soft Seat Valves – no audible leakage at 10% below nameplate set. At very low set pressures (20 psi and below), the ratio of the downward spring force as compared to the upward pressure force is very small. In these cases, it may be impossible to achieve seat tightness. Use soft seat valves for superior seat tightness in applications which fall within the soft seat material temperature limitations. Although soft seat valves will typically provide a higher degree of seat tightness than metal seats, Factory Standard does not ensure bubble-tight seats, regardless of seat material.
Maintenance should be performed on a regular basis. An initial inspection interval of no longer than 12 months is recommended. The user must establish an appropriate inspection interval depending on the service conditions, the condition of the valve and the level of performance desired.
The ASME Boiler and Pressure Vessel Code does not require nor address testing installed valves. The only thing the codes states are design and installation requirements, such as some valves must have a lifting lever.
For instance, for Section VIII: “Each pressure relief valve on air, water over 140F, or steam service shall have a substantial lifting device which when activated will release the seating force on the disk when the pressure relief valve is subjected to a pressure of at least 75% of the set pressure of the valve”.
Safety and safety-relief valves should be installed vertically with the drain holes open or piped to a convenient location. All piping must be fully supported.
Installing a safety valve in any position other than with the spindle vertical and upright may adversely affect performance and lifetime and may not meet code. Installation in any position other than vertical can violate code standards.