Caleffi 130 series low-lead brass manual balancing valves are used to measure and adjust the fluid flow rate in hydronic or plumbing circuits. The flow rate is directly determined from the pressure differential (from Venturi effect) measured across the two test ports. The valve design is fixed orifice with both pressure ports located upstream of adjustment plug and away from any pressure variations from turbulence as flow passes the adjustment plug - this feature makes pressure measurements and thus flow determination simpler and more accurate compared to variable orifice type balancing valves. Flow rate is calculated by simple formula or by easy reference to flow characteristic graph. Memory stop feature allows valve to be closed, and later reopened to the original set position. Teflon stem bearing guide prevents noise and vibration. The control stem threads remain dry at all times, and thus are not prone to seizing from scale after long in-operation periods. Stainless steel plug is highly resistant to erosion from fluid impurities.