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Hydraulic steering unit can make or break a trail machine

by:LIZHONG     2020-06-26
A poorly designed system or even a simple misuse of parts for a particular application can result in sluggish, hard-to-use steering unit - not to mention the ill effect on reliability. That's why we decided to delve into the subject of hydraulics and address a few common issues, while at the same time contrasting the two popular types of setups we see on the trail. We're going to break this somewhat complex topic into two categories. Traditionally, this has always been the point where most 'wheelers cross the line between a trail-only rig and a daily driver. This is because most people feel hydraulic systems are unreliable and therefore not suitable for the street. However, this is not necessarily true. Take a look at the heavy equipment industry: Caterpillar tractors, for example, rely on a variety of hydraulic systems to function, many of which control directional movement. Hydraulic steering unit systems have their place in several street-driving scenarios, too, though most are found on industrial or agricultural equipment operated at low speeds. These systems are engineered to perform a specific task within a specific range of parameters (i.e., speed, weight, temperature, and environment). The problem here - and probably part of the reason why fully hydraulic steering unit gets a bad rap on the street - is due to system design, or lack thereof. It all boils down to economics. No common man is willing to invest the millions it took Caterpillar to develop a fully hydraulic steering unit system reliable enough to pilot its dump trucks down the road safely. And because there are several sources for hydraulic steering unit components, all with very little 'specific information' about each particular application, it's hard for Joe Consumer to know which widget to install on his own rig. Full hydraulic steering unit requires eight major components: Each is equally important to the overall performance of the system. That's why it's most important to build a balanced or matched system. For most 'wheelers, the somewhat less expensive, less complex hydraulic assist may be the best option. In most cases, companies offer complete kits for specific vehicle applications like the PSC kit shown above for the '05 Jeep TJ. With an assist setup, your rig's mechanical steering unit remains intact, enabling the option of manual steering unit if the hydraulics should fail. We like this setup for trail rigs that are driven on pavement from time to time. Aside from helping your steering unit system push around larger meats, a ram assist can function as the ultimate steering unit dampener, too. At the same time, a ram assist also helps relieve stress on other steering unit components such as the steering unit box. The major difference between hydro-assist and fully hydraulic steering unit is that hydro-assist is basically a piggyback setup you add on to your existing steering unit system, while a fully hydraulic system is a stand-alone system relying completely on fluid power. This is the hydraulic fluid (or power-steering unit fluid) reservoir that stores the fluid necessary for the system. Think of it as an oil pan. Most power-steering unit pumps have a reservoir attached right to the pump body. The one shown here is a PSC part. At a minimum, the reservoir must be large enough to hold reserve oil for both extended and collapsed cylinder lengths. To figure out what you need, consider the oil volume-to-duty cycle ratio. In heavy equipment, this ratio is roughly 3:1, meaning your reservoir should hold three times the volume of the system. This is probably overkill for our purposes because this ratio was designed for 100 percent duty-cycle applications such as a bucket loader working at a strip mine that runs 24/7 all year long. A Jeep or buggy will typically see use on the weekends for recreational purposes only, so you really wouldn't need a 3-gallon power-steering unit reservoir. Keep in mind how often you use your rig and how much time the system will actually run once installed. In most cases, the supplier will have two or three different sizes of reservoirs to choose from. Similar in function to the automotive 'steering unit box,' this part translates driver input at the steering unit wheel to actual movement of the cylinder. Many people call them 'orbital valves.' This is incorrect. 'Orbital' refers to a specific type of hydraulic motor that has nothing to do with hydraulic steering unit. The hydraulic industry refers to these as steering unit control units (SCU) or, more commonly, metering valves. Metering valves have a specific displacement volume, which equates into how many cubic inches of fluid can pass through the valve in one 360-degree revolution. The rule on metering valves is: The higher-volume (in cubic inches) valve you get, the faster the wheels will cycle through the range of movement. Someone started a rumor about fully hydraulic steering unit being illegal for use on the highway. This is not true. We contacted the U.S. Department of Transportation and asked about the rules on hydraulic steering unit systems. We were told that any rules prohibiting the use of fully hydraulic steering unit systems in the automotive aftermarket would fall under local laws. We suggest you check with your state's local transportation authorities if you question the legality of hydraulics.
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