The Asco (previously Sirai) commercial pressurestat for 110~120/220~240V equipment, #P302-6. This is the part that regulates your boiler heating via a diaphragm that expands and contracts as the boiler steam pressure raises and lowers, activating the contacts and sending a signal to the heating element telling it to turn on or off. It is by far the most common pressurestat used historically and today.

European Espresso machine manufactures use British Standard Pipe fittings in their equipment. To measure a fitting, one measures the inside diameter of the male thread on a fitting. In most cases. Specialized fittings of course may have a wider or more narrow opening depending on the application and desired volume or flow rate through the fitting. But for the most part, it's the inside of a male fitting that is measured. A 1/4" Male BSP fitting will measure 13 mm (1/2") on the outside diameter, for what that's worth...

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TECHNICAL NOTES

• CE-SEV-ASE-UL approved
• ISO 228 G connection 1/4"M for pipe 4x6 mm
• adjustable scale 0.5~1.4 bar
• fixed differential 0.15 (0.06) bar
• fluid temperature max: 140° C
• max contact load: 220V 7KW (30A)

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Factory specification sheet click