It is an understatement to say that hose is merely an essential part of a hydraulic system. This is because over the years, the complexity of hydraulics has substantially increased. Hose dimensions have become smaller to accommodate tighter spaces, but at the same time, pressures are getting higher. A broad range of hydraulic hose featuring various styles are offered by numerous manufacturers. There are also thousands of fittings from which to choose. Although this wide variety of products can be advantageous, it can also make it difficult to determine which fittings and hoses are best. Below are some important aspects to which thought should be given when building a hose assembly:

The Application’s Dash Size or Inside Diameter

Hydraulic hoses are measured by their inside diameter– I.D.–which is also referred to as the dash size. Diameter is measured in sixteenths of an inch. In most cases, this measurement can be found on the hose’s layline, but can also be manually measured. The dash size is required in order to determine the system’s proper flow velocity. Too high of a flow will cause hose leakage, system damage, and pressure drops, while a sluggish performance can be expected if the flow is not fast enough.

Fortunately, your application’s proper hose I.D. can be determined with our flow capacity nomogram. Parker’s Hose Products Division has a full line of hose to fit various flow rates, ranging from size four to size forty.


Temperature is a critical factor when choosing a hose for your application, and you must consider both media and ambient temperature when making this decision. The temperature outside the hose is ambient temperature, while media temperature is the phrase used to describe the hose’s internal temperature. The hose’s overall temperature rating should not exceed the higher of the two. When selecting a hose, you should also give thought to the media type. This is because the temperature may be increased or decreased by certain media types. Therefore, some Parker hoses feature different fluid and temperature ratings. Both high and low temperature hoses are offered by Parker for specific applications.

Every Application is Different

When choosing a hose, thought must be given to how it will be used. The following questions are helpful when making this determination:

• Are there routing requirements?
• Must the assembly bear mechanical loads?
• Are there any environmental factors?
• What type of equipment is involved?

Specific requirements are set according to industry standards, including requirements for impulse cycles, burst pressure, tolerances, size and construction type. Parker is dedicated to meeting or exceeding standards set forth by the following organizations:

• International Organization for Standardization– ISO
• Deutsches Institute für Normung– DIN
• European Norm– EN
• Society of Automotive Engineers– SAE

Parker products are also manufactured according to government agencies’ requirements. Such agencies also regulate standards for ABS, the US Coast Guard, and other industries and organizations. The Parker hose line must not only meet the application’s functional requirements, but also the legal requirements set forth by the aforementioned agencies.

Bend Radius Requirements

A hose’s minimum bend radius refers to the smallest radius at which the hose may be bent without stopping the system from running at maximum pressure. Bending radius eases routing and enhances flexibility. Nevertheless, if the hose is bent below the minimum bending radius, possible hose failure may occur due to loss of mechanical strength. As a general rule, a minimum straight length of 1 1/2 times the hose’s outer diameter is allowed between the point where the bend starts and the hose fitting. For applications that require a tight bend radius Parker offers two products, the 797 and the 787 hose, both of which feature half the bend radius of a traditional SAE 100R15 hose.


The risk of abrasion is an important factor when choosing hose. To make a proper decision, you must consider the application’s external conditions and determine whether or not there is a risk of abrasion. The outside of most hoses feature neoprene; however, if it is inevitable that the hose will rub against machinery, materials, or against the boom or jib, a high abrasion carcass is the best choice. This is because hoses often wear through and ultimately fail when they continuously rub on the outside. Naturally, when this happens, pressure can no longer be contained in the hose and it will simply burst. Arguably, the number one cause of hose failure is external abrasion. Tough Cover–TC– is what Parker recommends for harsh environments, and for extremely abrasive environments, SuperTough–ST– is recommended.

Media Compatibility

Always consider media compatibility when selecting hose. The media being conveyed should be compatible with the hose’s inner tube, but it is also important to ensure compatibility with the O-rings, fittings and cover. Several problems to hydraulic systems and hose assemblies will occur if incompatible media is used. Avail yourself of our chemical resistance chart to check hose compatibility and prevent hose failures.

Pay Close Attention to Maximum Pressure Ratings

With regard to hose pressure, it is essential to consider the working pressure of the system, as well as spike pressures or surges. Such pressure should always measure below the hose’s designated maximum working pressure. Even though hydraulic hoses offered by Parker met a 4:1 pressure safety factor when tested, they are not designed for use at working pressures higher than those established for the assembly.

It is important to know the system’s exact maximum working pressure, which is that of its lowest rated component. For instance, even if the hose is rated to a pressure greater than the fittings, the entire assembly’s top working pressure is still that of the fittings.

Engineering specifications for pressure can be found on each hose, as well as on the hose’s laylines. We also offer a hose overview chart where you can find pressure specifications. For fittings, please see our Pressure Rating of Hose End Connectors chart.

The Complicated Process of Fitting Selection

The hose you choose must be compatible with the fitting-to-hose mechanical interface. Choose the appropriate mating thread to ensure leak-free sealing. The fittings that connect most hose types fall into one of two categories: field-attachable and permanent, the latter of which is primarily used in maintenance shops, by large-scale rebuilders, or by equipment manufacturers.

1. Permanent Fittings

Crimping machines are used to cold-form permanent fittings onto the hose. For this reason, permanent fittings are also sometimes referred to as crimped fittings. They are available for the majority of thermoplastic and rubber hoses and you can find a vast array of dependable connections for reasonable prices. Assemblies designed with portable machines in the field are typically uncomplicated systems that are both easy to operate and economical. Additionally, permanent fittings are not as difficult to install as other types.

2. Field-Attachable Fittings

Field-attachable fittings are categorized as clamp-type or screw-together. The screw-together fitting turns the outer coupling shell over the hose’s outside diameter, and thus attaches the hose to the fitting. The insert of the fitting must then be screwed into its shell. Thread type is another aspect to which thought must be given when selecting a fitting. Several thread types are available for hydraulic hose assemblies, including the following:

• Japanese fittings
• French Gas fittings
• British Standard Pipe–BSP
• German DIN hose fittings

In addition, one can choose from North American Thread Types, including those listed below:

• 4-Bolt Split Flange
• O-ring Face Seal–ORFS
• SAE O-rings–Boss Type
• Flange Fittings–Codes 61 and 62
• SAE 37⁰ JIC, SAE 45⁰ Flare
• Dryseal American Standard Taper Pipe Thread–NPTF

Ultimately, however, fittings are only as good as the person by whom they are installed. Each fitting style requires proper assembly procedures, and the level at which the assembler adheres to those standards is the difference between solid connections and future problems with the assembly. To ensure the correct identification is made, measure and compare the threads to the tables listed here.

Great resources are offered by Parker Hannifin for those in the market for hydraulic hose, equipment and fittings. These resources include information outlining proper techniques for hose assembly, as well as a mobile app called the Parker HoseFinder. The latter is another helpful tool for those with busy lifestyles who need assistance in selecting the appropriate fittings and hose for essentially any application.