Basic Hydraulics - Fluid Conductors

CHAPTER 11 - Fluid Conductors

Figure 11.1 - a charged bladder type accumulator

Overview

Transmitting power from one location to another is a key element in system design and performance. This transmitting of power is known as fluid conducting. Fluid conductors describe the different types of conducting lines that carry hydraulic fluid between components. The three principal types of plumbing materials used in hydraulic systems are steel pipe, steel tubing, and flexible hose. A safety factor of 4 to 1 is recommended on the pressure rating of the plumbing material. To determine the working pressure of the conductor, the rated burst pressure is divided by a safety factor of four.

Hose

Hydraulic hoses are used in applications where lines must flex or bend. When using hoses, system pressure, pressure pulses, velocity, fluid compatibility, and environmental conditions must all be considered. The Society of Automotive Engineers under SAE J5-17 has standardized hose construction. This is known as the R series (for example, 100R2 or 100R4). This designation describes the cover, construction, pressure rating, and application.

Hoses are usually pressure rated with a safety factor of 4 to 1. Different types and amounts of reinforcement give the hose specific pressure ratings. The reinforcement may be a natural or synthetic fiber or metal wire. The reinforcement may be braided or spiral bound. Required hose size depends on the volume and velocity of the fluid flow. Unlike pipe and tubing, hose sizes are designated by I.D. or inside diameter. Sizes are designated in 16ths of an inch by using a dash and a number equivalent to the numerator of the fraction.

Example: dash 8 (-8) or 8/16" or half inch I.D.

Hoses can last a long time, but all rubber slowly deteriorates with contact from various substances, such as solvents, water, sunlight, and heat. Hoses are not as permanent as metal conductors and should be replaced every few years.

Proper hose installation is critical. Improper bending, twisting, or lack of proper anchoring may

lead to hose failure.

Figure 11.2 - the correct and incorrect ways to install a hose

Pipe

Steel pipe is often a preferred conductor from the standard points of performance and cost; however, it is often difficult to assemble because welding is required to give maximum leak protection. It also requires costly flushing to ensure a contaminant free system at startup. Pipe is specified by its nominal outside diameter, but its actual flow capacity is determined by its inside area.

Figure 11.3 - a piece of hydraulic pipe

For example, Schedules 40, 80, and 160 and Double Extra have the same outside diameter, and can be threaded by the same pipe die. The difference is the inside diameter and area. Schedule 40 pipe is standard and has the thinnest wall, with more flow area but a lower pressure rating.

Figure 11.4 - a bourdon tube pressure gauge

Steel Tubing

Tubing is used as a conductor when rigid lines are required. It is often easier to assemble and form and requires no welding to achieve leak-free connections. As with all types of conductors, certain requirements must be met. The line must be large enough to carry the required flow and strong enough to withstand internal pressures. Figure 11.5 Hydraulic tubing.

Figure 11.5 - hydraulic tubing

Tubing is measured and specified by its wall thickness and outside diameter. Pressure ratings are based on tubing grade and wall thickness. One piece of tubing is joined to another tube connector, or component, with a tube connector and fastening nut. Often the tube is pre-flared to 37 degrees to accept a 37-degree flare connector.

Figure 11.6 - flaring diagram for hydraulic tubing

SUMMARY

Hydraulic hoses are used in applications where lines must flex or bend.

Pipe is specified by its nominal outside diameter, but its actual flow capacity is determined by its inside area.

Tubing is used as a conductor when rigid lines are required. It is often easier to assemble and form and requires no welding to achieve leak-free connections.

Basic Hydraulics - Check Valves

Basic Hydraulics - Accessory Components

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