Gearhead gospel: That "adjustable" claim ain't marketing. Crank the top nut while hot and actually SEE the blowoff pressure shift - try that with CNC-milled toys. This ain't no plumbing aisle trinket.
OKMO P70 Brass Impeller Pump - Scale Model Engine Parts 10.6MM Nozzle
OKMO T60 Brass Throttle Wheel - 22MM Throw Precision Engine Control
Microcosm M8-1 Adjustable Brass Safety Valve (M8*0.75 for Live Steam Equipment)
OKMO Microcosm M8 Mini Steam Engine Boiler Pump with Piston
JW-8 Brass Bell Whistle for Live Steam Engine M8×0.75 Adjustable Tone
Brass Bell Whistle for Live Steam Engine 1/4 to M8 Thread Options 92mm Long