What is the difference between an overflow valve and a pressure reducing valve?
4 Answers
The difference between an overflow valve and a pressure reducing valve: The overflow valve prevents system overload to ensure safety, while the pressure reducing valve reduces system pressure under the premise of ensuring the system does not overload. It can be said that the overflow valve works passively, while the pressure reducing valve works actively. The overflow valve is a pressure control valve, mainly used to control system pressure and also serves a unloading function. The pressure reducing valve is a pressure regulating valve that keeps the outlet pressure lower than the inlet pressure. Specific details are as follows: 1. Overflow valve: The inlet pressure of the overflow valve remains unchanged, and the inlet and outlet oil ports are not connected. The spool of the overflow valve moves from closed to open, and the overflow valve is basically internally drained. The oil on the pilot valve of the pilot-operated overflow valve is drawn from the inlet port. 2. Pressure reducing valve: The outlet pressure of the pressure reducing valve remains unchanged, and the inlet and outlet oil ports are connected. The spool of the pressure reducing valve moves from open to small (closed), the pressure reducing valve is externally drained, and the oil on the pilot valve of the pilot-operated pressure reducing valve is drawn from the outlet port.
Overflow valves and pressure reducing valves play different roles in hydraulic systems. The core function of an overflow valve is safety protection. It automatically opens when the system pressure is too high, releasing excess pressure to prevent equipment damage, much like in a car's braking system, where it prevents the master cylinder pressure from surging and causing lock-up. On the other hand, a pressure reducing valve is used to regulate pressure, continuously reducing high input pressure to a stable output pressure, ensuring smooth operation of subsequent components. For example, in a car engine's power steering system, it maintains constant pressure to reduce vibrations. In practical operation, their installation positions also differ: overflow valves are typically connected in series with the main system, while pressure reducing valves are often used in branched circuits. During everyday driving, improper operation may cause frequent activation of the overflow valve, signaling system overload; if the pressure reducing valve is not properly adjusted, steering feel may deteriorate. Regular inspection of these two components is crucial for car maintenance to prevent sudden safety issues.
From my experience in auto repair, the overflow valve acts more like an emergency exit in the system, releasing excess fluid when pressure exceeds limits, while the pressure reducing valve functions as a precision pressure regulator, specifically setting target pressure mid-pipeline. These two valves exhibit different symptoms when faulty: a broken overflow valve may cause hydraulic oil leakage or pump overheating, potentially triggering warning lights on the dashboard; a failed pressure reducing valve prevents proper pressure reduction, manifesting as soft brakes or heavy steering. You can perform preliminary checks yourself: start the engine to listen for abnormal noises and inspect for fluid leaks, but it's best to visit a professional shop for instrument-based pressure testing. Long-term neglect can damage the entire hydraulic system and increase repair costs. A simple recommendation is to conduct comprehensive valve inspections every two years - ensuring safety while saving money.
For example, the overflow valve is like an overflow hole on a bucket, automatically releasing excess water when it's too full to prevent the bucket from bursting; the pressure reducing valve is akin to a showerhead pressure regulator, adjusting water pressure to a comfortable level. In cars, they manage hydraulic pressure differences: the overflow valve releases pressure during overload, such as preventing engine overpressure bursts; the pressure reducing valve lowers high pressure to a set value, ensuring even and stable braking. Novice car owners don't need to understand the principles, just know that regularly changing hydraulic oil can prevent valve jamming. If problems arise, stop and repair promptly—safety first.
