An engineered water hammer arrestor must be placed _____ of the valve and as close to the valve as possible.

The correct placement of an engineered water hammer arrestor is on the supply side of the valve, very close to the valve itself. This positioning is critical because the water hammer arrestor is designed to absorb the shock of the water flow changes caused by the sudden stopping or starting of water movement, typically at faucets or valves. By being on the supply side, the arrestor can effectively mitigate pressure surges before they reach the valve, thus preventing potential damage to the plumbing system.

Positioning the arrestor immediately upstream of the valve allows it to function efficiently, as it can absorb the hydraulic shock from the water, reducing the likelihood of hammering noises and stress on the plumbing components. This is vital for maintaining the longevity and integrity of the plumbing system, as well as ensuring safe and smooth operation of fixtures and appliances connected to the water supply.

Choosing not to position the arrestor downstream or on the return side would diminish its effectiveness, as these locations would allow for the shock waves to impact the valve and plumbing fixtures before they are mitigated. Thus, situating the engineered arrestor on the supply side underscores its role in protecting the system from water hammer effects.