Because hydraulic circuits generate transients on valve closure and load reversal that reach several times nominal working pressure for a few milliseconds. A sensor rated only for the working pressure will be destroyed by those spikes, so overpressure and burst ratings are the figures that determine survival.

A damping orifice fitted in the pressure port that slows the transient reaching the sensing element, protecting it from spikes and reducing signal noise. It is worth fitting on any installation with fast valve closure or shock loading, at the cost of slightly slower response to genuine pressure changes.

Gauge, referenced to atmosphere, for most hydraulic work. Sealed gauge where atmospheric venting is impractical, such as submerged or sealed installations. Differential across a filter or heat exchanger, which is the standard way to detect a clogging element before it goes into bypass.

When only a threshold matters and no controller is involved - a simple interlock, a pump cut-out, or an alarm contact. A switch is cheaper and needs no analogue input. A transmitter is needed when the value itself, its trend over time, or proportional control is required.

4-20 mA where the run is long or electrically noisy, since a current loop is immune to voltage drop and resists interference; 0-10 V for short runs into equipment expecting it; CAN bus on mobile machinery. The receiving controller usually decides this rather than the sensor.

By showing what pressure is doing rather than only that it arrived. Slow build indicates pump wear or internal leakage, pressure that will not hold points to a valve or cylinder seal, and unexpected spikes reveal deceleration problems. None of that is visible on a gauge glanced at occasionally.

Periodically, especially where the signal drives a safety function or a commercial measurement. Drift is gradual, so a transmitter reading plausibly but incorrectly is more dangerous than one that has clearly failed - which is why scheduled verification beats replacing on failure.