A standpipe with a 2 1/2 pressure regulating valve shall be equipped with a ________ minimum drain riser.

A standpipe with a 2 1/2 pressure regulating valve shall be equipped with a ________ minimum drain riser.

• A. 2 inches
• B. 3 inches
• C. 1 inch
• D. 4 inches

Answer: (B)

When a standpipe includes a pressure-regulating valve, the drain needs enough capacity to handle the water that can exit the system without creating bottlenecks or backpressure. The valve reduces downstream pressure, but it doesn’t limit the amount of water that can flow out during discharge or hydrostatic testing. To prevent slow drainage, water hammer, or insufficient relief, the drain riser must be sized large enough to carry that flow. The standard minimum for this configuration is a three-inch drain riser, which provides ample cross-sectional area for draining. A two-inch drain would be too small to handle the expected flow, while a one-inch drain is far too small, and a four-inch drain goes beyond the required minimum.

When a standpipe includes a pressure-regulating valve, the drain needs enough capacity to handle the water that can exit the system without creating bottlenecks or backpressure. The valve reduces downstream pressure, but it doesn’t limit the amount of water that can flow out during discharge or hydrostatic testing. To prevent slow drainage, water hammer, or insufficient relief, the drain riser must be sized large enough to carry that flow. The standard minimum for this configuration is a three-inch drain riser, which provides ample cross-sectional area for draining. A two-inch drain would be too small to handle the expected flow, while a one-inch drain is far too small, and a four-inch drain goes beyond the required minimum.