How much force in kgf is needed to move a manual hydraulic lever?
There is no single number: the force follows the valve spring, the lever length and the state of the linkage. Measure peak force at the lever end.
There is no single number. The force required depends on the centring spring of the valve, on the spool friction, on the lever length and on the condition of the linkage; it can come out differently even on two machines of the same model. That is why the right method is not estimation but measurement: you hook a spring scale to the end of the lever and read the peak force that starts the movement.
What determines the force requirement
- Centring spring: the stiffer the spring that returns the spool to neutral, the heavier the lever.
- Lever length: a long lever requires less force, a short lever more. The same valve feels very different with different lever lengths; the relationship itself is explained in the definition of radial torque.
- Linkage: as intermediate joints, rods and bushings wear or corrode, friction increases.
- Oil temperature: cold oil makes the spool harder to move. A force value given without stating the measurement temperature is not comparable.
- Detent and lock: on detented valves where the lever locks in a position, the peak force needed to overcome the detent is markedly higher than the normal operating force.
How the measurement is made
- Start the engine and wait until the system reaches normal working temperature; cold oil makes the lever heavier and makes the measurement read higher than it is.
- Hook the spring scale to the end of the lever, at right angles to the plane the lever moves in.
- Pull the lever slowly in the direction of movement and read the highest value at the moment movement begins.
- Measure each direction separately; usually one direction is heavier than the other.
- On a detented valve, note the peak value that overcomes the detent separately.
If you pull the scale from the middle of the lever rather than from its end, the value you read comes out low and misleads you; take the measurement at the point where the actuator will be attached.
It is worth taking the measurement both with the oil cold and after it has warmed up, and noting both values down. The kit has to work in either case; an installation that cannot move the lever at the first start in the morning is inadequate even if it works properly in the afternoon. Base your choice on the higher of the two values.
Choosing the kit after measuring
The value you measure is not an approval but a point of comparison; what is looked at is the margin left between the measured force and the kit capacity.
| Measured peak force | Assessment |
|---|---|
| Well below the kit capacity | There is margin; it can be applied directly |
| Close to the kit capacity | Service the lever mechanism first, then measure again |
| Above the kit capacity | Not applicable; installation is not started before the force requirement is brought down |
The HCT400 servo applies 15 kgf and the HCT402 about 20 kgf. Which levers that difference is useful on is dealt with under where the force difference matters.
If the measurement comes out close to the limit
The force capacity of the kit you choose should leave a margin above the measured peak force. If the measurement comes out very close to the limit, the right step is to service the lever mechanism first; a lubricated, clean and free lever both demands less force and runs more stably. Go over the joint bushes, the pins and the return spring, clean the corroded surfaces and repeat the measurement. A force requirement that servicing does not bring down is the valve's own characteristic and cannot be made up for on the kit side.
In short: measure with hot oil, from the end of the lever and separately for each direction, and take the highest value as your basis. Choose the kit against that single number and leave a margin between the force value in the catalogue and the value you measured. Repeat the measurement whenever a part in the valve or in the mechanism changes: a new centring spring, a new joint or a connection that has been taken apart and refitted can change the weight of the lever without anything being visible.
The full topic: HCT402 technical review: what, how and how much