Choosing a P120 Monoblock Valve for Large Tractors

The P120 monoblock valve is the high-flow version of the P series by KYDAC. As a monoblock valve it achieves up to 120 L/min at 250 bar from a single cast-iron body and is suitable for 1 to 7 working sections. Therefore, this valve is particularly suitable for large tractors, combine harvesters and wheel loaders with high pump output greater than 80 L/min.

Match the valve to the flow delivered by the pump. When properly sized for the system flow, the valve can help avoid excessive pressure drop and unnecessary restriction. Any monoblock valve such as the P120 can therefore be initially determined by two criteria: the amount of oil that the pump delivers and the number of functions that the machine is intended to perform. Final selection should also confirm the circuit type, spool function, port configuration and pressure requirements.

What the P120 Monoblock Valve Handles

Flow is the main parameter for this valve. The P120 monoblock valve is specified for 120 L/min nominal flow and a maximum working pressure of 250 bar. The body is cast iron and there are 1 to 7 working sections depending on the number of functions a machine is specified to perform.

The P120 valve is rated for an ambient temperature range between -40°C and +80°C and covers a range of oil viscosities from 12 cSt up to 400 cSt. Select an oil grade which will maintain viscosity within this range at the temperatures encountered by your equipment. This will include cold start up during winter and heavy service during summer.

Pressure is a design limit like flow, it’s not a point to tune. The fact that this valve is rated 250 bar is only relevant to typical mobile circuits, and then only in relation to the required pressure from the load and the relief setting, not from the name of the valve. Simply choose a valve with sufficient rating for the system and then let the relief valve do its job and protect the circuit.

The P120 is a high-flow hydraulic valve, the biggest in the KYDAC P series of hydraulic valves. The P80 and P40 are the smaller brothers, all made of cast iron and described on this page about KYDAC P series monoblock valves.

When 120 L/min Starts to Matter

Flow determines body size. Above 80 L/min through the hydraulic valve, the P80 starts to limit flow and a P120 hydraulic valve is usually more suitable. Large implements such as folding harrows, large ploughs and grab loaders require higher flow to reduce the time needed by the cylinder to complete a cycle.

There is one caveat to be aware of. A valve will only allow to pass as much liquid the pump is actually able to pump. A 120 L/min body fitted to a 70 L/min system will still receive only the flow supplied by the pump. The larger valve does not create additional flow, so its extra flow capacity may provide little practical benefit. In essence, a larger body costs more than the corresponding benefit. Therefore, always size to the pump and not to the nameplate!

The P120 is a valve for high-horsepower tractors, self-propelled harvesters and large wheel loaders. The rear remote banks on these machines usually require more flow than a mid-range valve can meter cleanly and the P120 leaves plenty of headroom.

It’s a case of slow extension/retraction of a large plough or folding harrow across a field and more flow through the valve enables the cylinder to fill up faster for a given cylinder size. A larger-bore cylinder requires more flow to achieve the same speed. However, the benefits are only realized if the pump and associated hoses are able to deliver the additional flow.

P120 Next to the P80 and P40

These valves are all ‘close cousins’ made from cast iron as monoblock directional control valves rated for 250 bar operation with 1 to 7 sections. The difference between them is flow rate. The P40 is rated for 40L/min, the P80 for 80L/min and the P120 for 120L/min. The operating pressure and general construction of the valves remain the same for all three sizes.

Use a P120 when the machine is running at a higher flow than the P80 and attachments are cycling too slowly. Use a P80 on tractors and loaders that are feeding it with 80 L/min or less. The smaller body of the P80 costs less and may be the more economical choice when system flow remains within its rated range.

Monoblock Build and Field Behavior

The monoblock valve is a single cast iron casting. The spool bores and pipe connections are machined into a single block. There are no bolts holding the various circuits together. A machine that vibrates all day creates a lot of external forces that can cause leaks, and a single cast iron casting eliminates the sealing joints between stacked valve sections, reducing the number of potential external leakage points.

The shock loads from a back to back mounted directional valve are absorbed by the cast iron. A strong body helps to maintain the alignment of the bores and mating surfaces. These surfaces are subject to shock as the spools cycle under full pressure shift after shift.

We at KYDAC have the spools ground to a precise fit within the bores to prevent internal bypass. The only thing to be aware of when ordering a monoblock is that once it has been delivered and installed it cannot be restacked into a different number of sections. If in doubt it is always better to go with a sectional valve body which can have more functions added at a later date.

Sizing and Replacement Notes

Two numbers initially size the valve: pump flow and function count. Flow picks the body, whether P40, P80, or P120. Function count sets the sections, and lift, tilt, dump, and each rear remote usually takes one spool. Final selection should also verify circuit type, spool function, ports, control method and pressure requirements. For a broader view, KYDAC also builds sectional and other directional control valve designs for multi-circuit work.

Be sure to properly care for the removal of your imported monoblock. A P120 for example is not going to simply drop into a YUKEN, REXROTH, or VICKERS unit. Verify port location and threading, unit mounting dimensions, circuit type, spool function, pressure and flow before you order what seems to be a same-spec P series replacement part. Some circuits are able to use a P series part for replacement, but again this must be verified against your part print rather than the catalog page headline.

Conclusion

A single body type is selected based on flow. Thus a tractor or combine supplied with more than 80 L/min can get more from a P120 monoblock valve than from a mid-range P80 model. However full-speed running of cylinders depends on the pump delivering the required flow. The P120 valve carries 1 to 7 sections at 250 bar. Ambient temperature range is -40°C up to +80°C. Operating oil viscosity is in the range 12 to 400 cSt.

When more than 120 L/min are required in a particular circuit, the KYDAC DCV series can be provided with higher flow rates and greater numbers of spools to form large multi-circuit units. We check the fit based on the pump rating and the number of spools provided.

FAQ

Q: Which machines need a 120 L/min monoblock valve?

Large tractors, combine harvesters and large wheel loaders usually operate above the P80 flow rate of 80 L/min. The P120 valve is usually the better option for these machines. However, the most important factor is the flow output of the pump. If the system frequently moves more than 80 L/min then a larger valve will maintain cylinder speed and minimize pressure drop. If the system rarely moves more than 80 L/min then the leaner P80 valve may be the better option.

Q: Can a P120 replace a YUKEN, REXROTH, or VICKERS monoblock?

Some circuits are interchangeable with P120, but you must confirm the detail interchange on port layout and threads, mounting, circuit, spool function etc. including pressure and flow. The P120 is same spec where it does interchange, but not a simple ‘drop in’ where it does not. Confirm on the drawing.

Q: How many sections can the P120 carry?

The P120 is available with 1 to 7 working sections. Count the functions the machine runs, such as lift, tilt, dump, and each rear remote, and that usually sets the count. A monoblock body cannot be re-stacked later, so order the number of sections you need from the start.

Q: What warranty and quality standard back the P120?

KYDAC manufactures the P120 valve according to its quality management process and backs up the valve with a 2 Year Warranty. Please refer to below information for sampling, lead time, OEM and ODM services, etc. And the above information will be confirmed once we receive your detailed specification.