If resistance to flow increases in a hydraulic circuit, what is the typical effect on pressure?

• A. Increase pressure
• B. Decrease pressure
• C. No effect
• D. Decrease temperature

Answer: (A)

When flow meets a throttling resistance, there is a pressure drop across that resistance that is proportional to the flow rate. In formula terms, the pressure difference across the element is ΔP = Q × R. If the resistance R increases and the system tries to push the same amount of fluid (the flow Q is roughly held by the pump or load), the pressure difference must become larger. To maintain the same flow through the tighter restriction, the pump or upstream part of the circuit must generate higher pressure. So the typical effect is that the pressure upstream of the resistance rises (the pressure needed to overcome the higher resistance increases).