Throttling a pump against a gate valve should be avoided because it will ________.

• A. Increase flow
• B. Improve pump efficiency
• C. Damage the gate valve and increase costs
• D. Decrease headloss

Answer: (C)

Gate valves are designed to be fully open or fully closed, not to regulate flow. When you throttle a pump by partially closing a gate valve, a large pressure drop occurs across the valve. This creates high flow velocity and turbulence through the valve, which wears and erodes the valve seats and seals, can cause packing leaks, and may lead to valve sticking or failure. At the same time, the pump has to work harder to push against the restriction, pushing it away from its optimal operating point and increasing energy use and wear. All of this translates into higher maintenance and replacement costs. For proper flow control, use a valve designed for throttling (like a globe or control valve) or adjust the pump speed.