Size is based on the measure of a hose’s Inner Diameter (I.D.) in sixteenths of an inch. (The exception to this is SAE 100R5 hose.) This measuring system of the inside diameter of the hose is universally used by the ﬂuid power industry today. Don’t know the hose size? Check the layline. If the original printing has worn off, the original hose must be cut and the inside diameter measured. Be sure to measure the overall assembly length and ﬁtting orientation before cutting the hose.
The hose I.D. must be sized accurately to obtain the proper ﬂow velocity. A ﬂow that’s too slow results in sluggish system performance, while a ﬂow that’s too high causes excessive pressure drops, system damage, and leaks.
When specifying hose, there are two temperatures you need to identify.
1) Ambient Temperature, which is the temperature that exists outside the hose where it is being used.
2) Media Temperature, which is the temperature of the media conveyed through the hose.
Very high or low ambient temperatures can have adverse affects on the hose cover and reinforcement materials, resulting in reduced service life.Media temperatures can have a much greater impact on hose life. For example, rubber loses flexibility if operated at high temperatures for extended periods.
Parker hoses carry different temperature ratings for different ﬂuids. For example, 811HT hose has a temperature range of -40°F to + 257°F (-40°C to +125°C) for petroleum-based hydraulic ﬂuids. However for water, water/glycol, and water/oil emulsion hydraulic ﬂuids, the range drops to a rating of up to
+185°F (+ 85°C). Air is rated even lower at up to 158°F (+ 70°C).Some media can increase or decrease the effects of temperature on the hose.
Before selecting a hose, it's important to consider how the hose assembly will be used. Answering the following questions may help:
• What type of equipment is involved?
• What are the environmental factors?
• Are mechanical loads applied to the assembly?
• Will the routing be conﬁned?
• What about hose ﬁttings – permanent or ﬁeld attachable?
• Will the assembly be subjected to abrasion?
What will the hose convey? Some applications require the use of specialized oils or chemicals. Consequently, the hose you order must be compatible with the medium being conveyed. Compatibility must cover not just the inner tube, but the cover, hose ﬁttings, and o-rings as well. Use the Chemical Resistance Chart found in Section E to select the correct components of the hose assembly that will be compatible with a system’s media. The chart contains the chemical resistance rating of a variety of ﬂuids.
When considering hose pressure, it’s important to know both the system
working pressure and any surge pressures and spikes.Hose selection must be made so that the published maximum working pressure of the hose is equal to or greater than the maximum system pressure. Surge pressures or peak transient pressures in the system must be below the published
maximum working pressure for the hose.
All Parker hydraulic hoses have passed the industry rated speciﬁcations
for burst pressure and carry a 4:1 safety factor unless otherwise noted. Burst
pressure ratings for hose are for manufacturing test purposes only. They are not an indication that the product can be used above the published maximum working pressure.
Care must also be taken when looking at the “weakest link” of the hose assembly. A hose assembly is rated at the maximum working pressure of the hose and the ﬁtting component. Therefore the maximum working pressure of the hose assembly is the lesser of the rated working pressure of the hoseand the end connections used.
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