How to Choose a Proper Hose

Resource Description

How to Choose a Proper Hose

INTRO

A Hose is a flexible and often reinforced tube used to transfer fluids from one location to another. Industrial hoses cover the broad range of fluid transfer lines, including flow lines for fluids and gases in pneumatic, hydraulic, or process applications, as well as specialized uses in heavy industry, such as mining, geotechnical, and construction. Industrial hose is usually application-specific; consultation with hose manufacturers regarding specific applications is typical.

Hoses are usually constructed using 3 basic parts:

  • A plastic or rubber tube or inner lining which makes contact with the fluid.
  • A textile, plastic, or metal body or carcass which reinforces the structure of the hose to withstand internal and external pressures.
  • A rubber, plastic, metal, or textile cover, which protects against damage due to wear, abrasion, and the environment.

7 STEPS TO SELECT A PROPER HOSE

An effective way to remember hose selection criteria is to remember the word…

S T A M P E D

S = Size

T = Temperature

A = Application

M = Material (or Media)

P = Pressure

E = Ends of couplings

D = Delivery (velocity & volume)

 

1. Hose SIZE (Dash Numbers)

The inside diameter of the hose must be adequate to keep pressure loss to a minimum and avoid damage to the hose due to heat generation or excessive turbulence. See hose sizing Nomographic chart. To determine the replacement hose size, read the layline printing on the side of the original hose. If the original hose layline is painted over or worn off, the original hose must be cut and the inside diameter measured for size.

Hose cut

NOTE: Before cutting an original hose assembly, measure the overall assembly length and fitting orientation. These measurements will be required to build the replacement assembly.

The hose ID 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.

The hydraulics industry has adopted a measuring system called Dash Numbers to indicate hose and coupling size. The number which precedes the hose or coupling description is the dash size (see the table below). This industry-standard number denotes hose ID in sixteenths of an inch.

 

All except Transportation and Refrigerant Hoses

Transportation and Refrigerant Hoses

Dash No.

Inches

Millimeters

Inches

Millimeters

-3

3/16

5

--

--

-4

1/4

6.3

3/16

5

-5

5/16

8

1/4

6.3

-6

3/8

10

5/16

8

-8

1/2

12.5

13/32

10

-10

5/8

16

1/2

12.5

-12

3/4

19

5/8

16

-16

1

25

7/8

22

-20

1-1/4

31.5

1-1/8

29

-24

1-1/2

38

1-3/8

35

-32

2

51

1-13/16

46

-40

2-1/2

63

2-3/8

60

-48

--

--

3

76

 

Hose OD can be a critical factor when hose routing clamps are used or hoses are routed through bulkheads. Check individual hose specification tables for ODs.

 

2. TEMPERATURE

Hose max/min temperature

When specifying a hose, there are two temperatures you need to identify. One is the ambient temperature, which is the temperature that exists outside the hose where it is being used; the other is the media temperature, which is the temperature of the media conveyed through the hose.

Very high or low ambient temperatures can have adverse effects 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. Different hoses carry different temperature ratings for different fluids. Some hoses have 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 materials/media conveyed can increase or decrease the effects of temperature on the hose. The maximum rated temperature of a hose is specific to the material/media.

 

3. APPLICATION

Before selecting a hose, it is important to consider how exactly the hose assembly will be used. To fulfill the requirements of the application, additional questions answered, 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?

Hoses (abrasion-resistant)

Sometimes specific applications require specific hoses. For example, applications where hoses will encounter rubbing or abrasive surfaces, would be best handled by the abrasion-resistant hose.

When application space is tight, the bend radius is another important consideration. Hoses with increased flexibility and smaller outer diameter allow faster, easier routing in small spaces, reducing both hose length and inventory requirements. Industry standards set specific requirements concerning construction type, size, tolerances, burst pressure, and impulse cycles of hoses such as:

  • SAE (Society of Automotive Engineers)
  • EN (European Norm)
  • DIN (Deutsches Institut für Normung)
  • ISO (International Standards Organization)

 

4. MATERIAL / MEDIA

Think about what the hose will convey. Some applications require specialized oils or chemicals to be conveyed through the system. Consequently, hose selection must assure the compatibility of the hose tube, cover, couplings, and O-rings with the fluid (material/media) used. Additional caution must be exercised in hose selection for gaseous applications, such as refrigerants and LPG.

NOTE: All block type couplings contain nitrile O-rings that must be compatible with the fluids being used.

 

5. PRESSURE

presure

The pressure rating defines the force per unit area that can be exerted on the hose or vessel during operation, typically measured in pounds per square inch (psi).

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.

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 minimum of the rated working pressure of the hose and the end connections used. For example, if the hose has a pressure rating of 7,500 psi but a quick-coupler fitting has a pressure rating of only 4,200 psi, the pressure rating for the assembly is 4,200 psi.

6. ENDS of Couplings

Identify style, type, attachment method, pressure rating, and material compatibility of end couplings and connections. Once thread ends have been identified, consult the appropriate section of the catalog for specific part number selection.

7. DELIVERY (Volume and Velocity)

If the same ID of the original hose is used, assume the system is properly sized to efficiently transport fluid. If the system is new or altered, determine the hose ID needed to transport required fluid volume flow by using the Nomographic Chart.

Pressure Spikes

also - Pressure Control

Pressure spikes can occur during machine operation in an instant. They can occur so quickly in fact, that standard glycerin filled gages will never detect them. Using Pressure Controllers can help detect how often and how drastic these pressure spikes are.