A worn pump delivers less flow at a given pressure without any dramatic symptom - cycle times simply lengthen. Measuring flow at a known pressure and comparing against the original figure quantifies the loss directly, which is how a decision to overhaul is made on evidence rather than on suspicion.

Gear and turbine meters for accuracy in reasonably clean systems, accepting that they have moving parts to wear. Variable-area and spring-loaded piston types for rough service and permanent installation where robustness matters more than precision. Ultrasonic or Coriolis where accuracy or an unobstructed path justify the cost.

On most meter types, yes, and hydraulic oil viscosity changes substantially with temperature - so a meter calibrated warm reads differently cold unless it compensates. For meaningful comparison over time, either use a temperature-compensating meter or record oil temperature alongside every reading.

Wherever the answer is needed, but with attention to added pressure drop. Any meter is a restriction, and on a pump suction line or a return line that restriction can cause cavitation or raise back-pressure beyond what a case drain or motor seal tolerates. Pressure lines are generally the safest location.

For diagnosis, a portable test kit measuring flow, pressure and temperature together is far more useful and serves many machines. Permanent meters suit control applications and continuous monitoring of a critical circuit. Many operations run a portable kit for troubleshooting and permanent sensors only where control requires them.

It can, though in practice actuator speed is more often controlled by valve position or by measuring position and differentiating. Flow feedback is used where volume delivered matters directly, and where the actuator's own position is not accessible to measurement.

It applies a controlled back-pressure so a pump can be tested at a realistic working pressure rather than free flow. Flow figures only mean something at a stated pressure, since a worn pump may deliver near-full flow unloaded and far less once it has to work - which is exactly what the test is looking for.