Set the regulator, then read the case drain.

The four signals the regulator reads

Every K3V / K5V regulator is a small servo bolted to the top of the pump group. It tilts the swashplate so the torque draw never exceeds the engine's rated horsepower. It reads four pressures; if any signal is missing or wrong the pump will behave like a failed regulator even when the regulator is fine.

Five checks before the cap comes off

• Engine reaches rated high idle. If it only makes 1,900 instead of 2,050 min⁻¹, the torque limit is not the regulator's fault.
• Oil at 45–60 °C. Adjusting on cold oil leaves the machine over-fuelling once it warms up.
• Pilot pressure 35–40 bar with the joysticks centred.
• EPPR coil 20–30 Ω cold. An open coil forces minimum torque.
• Pn line intact: crack the fitting, oil must weep at low pressure with the sticks centred.

Q1 and Q2, with the numbers

Q1 limits maximum displacement; clockwise reduces flow. Roughly a quarter turn is 3–5 % of maximum flow. Never move more than a full turn before re-testing.

Q2 sets residual flow at idle. It is factory-locked; break the lock-nut only if standby pressure stays above 40 bar with everything centred. After any adjustment: cap on, warm to 55 °C, stall test for no more than 5 s — RPM must not drop more than 200 below rated.

The case-drain test

• Warm to 55 °C. Leakage on cold oil reads misleadingly low.
• Plumb a 0–40 L/min turbine flowmeter into the case-drain hose, before the return filter.
• Baseline with sticks centred: a healthy pump is under 2 L/min.
• Deadhead for 5 seconds only (bucket curled, against the relief), read the loaded flow, release immediately.
• Loaded drain that rises to 10–15 % of pump flow means the rotating group is done — rebuild or replace, not adjust.

One condition before you buy anything: a regulator tune is only legitimate after these numbers are recorded. Send the four pressures and the case-drain flow with the machine model and we will tell you which of the three outcomes it is.