Excavator Control Valve Flow Sharing Adjustment: How to Split Pump Output Between Functions
When you pull two levers at the same time on an excavator, the pump is sending 200-plus liters per minute into the control valve. That flow has to get split between two circuits. If the valve splits it 60-40 instead of 50-50, one cylinder runs fast and the other crawls. The operator notices it immediately — the machine feels lopsided, cycle times suffer, and productivity drops.
Flow sharing is not a mystery. It is a mechanical function inside the main control valve, and it is adjustable. Most technicians never touch it because they do not know where the adjustment lives or how to verify it without a proper gauge setup. This guide covers the actual method — what to check, what to turn, and how to confirm the split is balanced.
How Flow Sharing Actually Works Inside the Valve
The main control valve has a flow-sharing spool or orifice inside each section. When one lever is pulled, that section gets priority flow. When a second lever is pulled, the flow-sharing circuit redirects a portion of the pump output to the second function.
The ratio is not fixed. It depends on spool position, orifice size, and spring force. On most valves, the default split under equal lever input is roughly 60 percent to the first function and 40 percent to the second. That bias exists by design — the first function you pull is supposed to get more flow. But when the bias drifts to 70-30 or worse, the machine becomes frustrating to operate.
Three things throw off the flow split.
The flow-sharing orifice wears. This is a small drilled hole, typically 0.8 to 1.5 mm, that meters how much flow goes to the secondary circuit. Over time, the edges erode and the hole gets bigger. More flow leaks to the secondary side, starving the primary function.
The flow-sharing spool clearance increases. When the spool-to-bore clearance exceeds 0.015 mm, oil bypasses the metering edge instead of going through the orifice. The flow split collapses, and both functions get less than they should.
The compensator spring drifts. The pressure compensator in each section adjusts flow based on load. If the spring weakens, that section opens wider under load and steals flow from the other circuit. The result is one function that accelerates while the other slows down mid-stroke.
Preparing the Machine Before Any Flow Adjustment
Warm Oil Is the Foundation
Cold oil gives you a false flow split. Viscosity at 40 degrees Celsius makes every orifice restrict more than it should. You will tune the valve with cold oil, get a 50-50 split on the gauge, then watch it drift to 60-40 the moment the oil hits 55 degrees. That is not a bad valve — that is cold oil doing what cold oil does.
Run the engine at high idle for at least 15 minutes. Hydraulic oil must reach 50 to 55 degrees Celsius. Every number in this guide assumes warm oil. No exceptions.
Lock Everything Down
With the engine at high idle, move all levers to neutral and lock them. Cycle each lever five times to bleed trapped pilot pressure. Disconnect the battery near solenoid connectors. Any stray pilot pressure shifts the main spool partially open, which changes the flow dynamics through the sharing circuit and gives you a reading that means nothing.
You need two pressure gauges for this job. One on the cap-end line of the primary cylinder, one on the cap-end line of the secondary cylinder. Both gauges must be rated for at least 40 MPa. Install them on the test ports at the valve block, not on the cylinder — cylinder-side readings include line losses and will mislead you.
Finding the Flow-Sharing Adjustment Point
Where the Adjustment Lives
On most excavator main control valves, the flow-sharing adjustment is a screw on the side of the valve block, near the junction between two sections. It controls a spring-loaded poppet or a sliding sleeve that meters how much flow passes from the primary circuit to the secondary circuit.
Turn the screw clockwise to restrict flow to the secondary side. This gives more flow to the primary function. Counterclockwise opens the metering edge wider, sending more flow to the secondary side. One full turn typically changes the split by 5 to 8 percent. Always work in 1/8 turn increments.
Some machines use a set of shim washers instead of a screw. If your valve uses shims, you change the flow split by swapping the shim for a thicker or thinner one. A thicker shim restricts flow more. A thinner shim opens it up. Shim changes are permanent — you cannot fine-tune with shims the way you can with a screw.
The Flow Meter Method
If you have access to a flow meter, use it. Connect one flow meter to each cylinder line. Pull both levers to exactly 50 percent travel simultaneously. Read both flow meters. The split should be within 5 percent of equal — so if the pump is putting out 240 liters per minute, each circuit should get 115 to 125 liters.
If one side reads 140 and the other reads 100, the flow split is off by 15 percent. That is enough to make the machine feel unbalanced. Turn the flow-sharing screw clockwise on the side that is getting too much flow. This restricts that side and pushes more flow to the other circuit.
Wait 10 seconds after each turn for the flow to stabilize, then re-read both meters. The goal is both meters reading within 5 percent of each other at equal lever input.