HydraForce Insider Blog

What if I told you I could design a hydraulic system that functions the same or better than your current system, but with less cost, less space requirement, fewer leak points, better appearance and less assembly and installation time? First of all, would you even believe me? Secondly, why aren’t you doing it already?

  Another benefit of a manifold design is the attractive appearance. It’s compact and shiny, and can be anodized any colour you wish. They leave you wondering what’s inside, and are great for keeping competitors from seeing how your system is plumbed together. Have a look at the photo on the right; does your hydraulic system look that good?

A cartridge valve’s function is represented with an ISO standard hydraulic symbol that characterizes the function that the valve performs.  In our many product pages, you can find many unusual valves with very peculiar and complex hydraulic symbols that appear to contain an entire small hydraulic circuit.  In this post I will discuss the principle beyond combining cartridge valves and provide a few practical examples that may help you save money when you are designing a hydraulic circuit.

Last time we discussed how to make a flow divider with separate cartridges.  If this was of interest the following goes a little deeper into this subject and shows how to maximize the versatility and address general flow divider issues.

First off, it’s worth noting that unlike Flow Sharing the pump itself does not have to be load sensed if all flow is to be utilized in a stand-alone circuit.

Are you looking for an alternative for your Flow Divider circuit that will address the issues of multiple division, irregular percentage splits, adjustable ratios, inlet flow variance versus accuracy and pressure drop?  If so, an alternative works for dividing pump flow only.  If you need combining too, you might have to stick with the traditional flow divider / combiner (or read next week’s article to see a combining solution). 

While there are many uses for L.S. priority valves, typically they are used to provide priority flow and/or pressure to certain components or functions depending on need. One of the most common uses is to apply them with L.S. steering orbitals.
The two most common types of L.S. steering orbitals (Static and Dynamic) are shown below. We use a static L.S. priority valve (ECxx-42) with a static steering orbital and a dynamic L.S. priority valve (ECxx-43) with a dynamic steering orbital. Notice the direction of the sense flow.

Static Steering Unit

In a static steering system, the sense flow goes from the steering orbital to the EC valve. The faster you turn the steering wheel, the more flow comes out the work ports.

There are several variable orifices in the steering orbital, which open and close proportionally based on how fast you spin the wheel. In neutral, the sense pressure vents to tank through the steering unit.

Dynamic Steering Unit

In a dynamic steering system, the sense flow goes from the EC valve to the steering orbital and back to tank through the variable bleed orifice in the steering orbital.

Turning the steering wheel opens the work ports and closes the bleed-off orifice, thus building pressure in the sense line pushing on the EC spool. This directs more oil to the orbital the faster you spin the wheel.

Most Steering Circuits Utilizing Orbitals Use a Dynamic Setup

Since the steering unit is really just a rotary style variable orifice, using a pre-compensator in conjunction with it makes the steering function compensated. With a given steering RPM, the flow will remain constant regardless of varying load pressure.

The boost orifice needs to be located in the shown position to prevent slow movement of the EC spool when the RV opens, thus preventing a pressure spike.

The objective is for the steering to work perfectly with as little pressure drop as possible, however sometimes we need to fine tune the responsiveness or the maximun steering flow by tweaking a few things.

Ways to Fine-Tune the Circuit to Optimize Steering Performance

The pressure differential between the EC valve and the L.S. port of the steering unit is called the margin pressure. This pressure differential controls the responsiveness and the maximum steering flow. This is determined by a combination of the bias spring of the EC and boost orifice.

The dynamic L.S. priority valves have two orifices in the spool, one for damping (PP), and the other for feeding (DS) oil to the orbital. The pilot flow to the L.S. port of the steering unit is determined by the spring value and the feed orifice. The spring value is typically either 80 psi or 100 psi, while the orifice is typically between 0.020" and 0.031" Dia., depending on which size EC valve you are using.

You can create any margin pressure you want by simply increasing or decreasing the size of the boost orifice. The smaller the orifice, the higher the margin pressure.

Pressure drop data from a steering unit catalog will help determine what is required to achieve the flow you need. However, the responsiveness or optimum feel is typically determined by an expert operator. By increasing or decreasing the boost orifice, you will be able to fine-tune the responsiveness or feel of the steering wheel.

An increase or decrease of as little as 0.002" Dia. can make a huge difference in the steering feel. Margin pressure that is too low will result in steering that is slow and sluggish. Margin pressure too high will result in jerky steering.

Proportional Steering and On/Off Lift Circuit

It is common to use proportional valves instead of steering orbitals to steer many types of equipment. This circuit simply gives priority to steering while allowing the excess flow to lift and lower a cylinder. The EC valve not only gives priority to steering, it also compensates the proportional valve so the same current value will achieve the same flow regardless of load.

Priority Valve Working with Manual Valve

It is becoming more common to use an EC valve mounted to the inlet of a manual valve to give priority to certain functions while also limiting the maximum flow and pressure to those functions.

Typical Priority-on-Demand
Flow Control Circuit

Most uses of the L.S. Priority Valves are for flow control. By sensing downstream of a fixed or variable orifice, you can compensate the circuit. The needle valve shown above could be any one of a number of components such as a ball valve, proportional valve, on/off valve or a simple orifice.

Pressure Control Valve

Many people don't realize you can use an
ECxx-42 or ECxx-43 to create a pressure control. Think of this as a pressure reducing valve with an excess flow port. The valve will modulate to maintain the spring value in the priority (CF) leg regardless of flow and/or the downstream pressure and flow in the bypass leg. Higher spring pressures can be achieved by using an ECxx-43 and boosting the sense line with an orifice or relief valve.

Most of you reading this know the common benefits of hydraulic cartridge valves (click here for an excellent refresher). However, there are several key benefits routinely overlooked or misunderstood throughout the industry. HydraForce has dedicated significant efforts to innovation in cartridge valve technology — including the consolidation of multiple valve functions into a single cartridge, higher pressure and flow ratings, and improved machine control solutions.