11.11 Perssure Control

Question 1

why are relief valves used in a hydraulic system?

Answer 1

to ensure a safe constant predeturmined maximum pressure in a system

Question 2

what are the most common types of pressure relief valves in a hydraulic system ?

Answer 2

-ball type
-sleeve type
-poppet type

Question 3

when a pressure relief valve is incorperated as a system relief valve what is this for ?

Answer 3

as a safety device incase of a failure in the pump or other pressure regulating devices

Question 4

when a pressure relief valve is incorperated as a thermal relief valve what is this for ?

Answer 4

used to reliefe excessive pressure due to thermal expansion of the fluid.

Question 5

what is a thermal relief valve usually used in conjunction with?

Answer 5

when a check valve or a selector valve prevents pressure from being relieved throughthe main pressure relief valve

Question 6

what is the purpose of a pressure regulator?

Answer 6

to manage the output of the pump to maintain system operating pressure. and to permit the pump to turn without resistance

Question 7

what is the purpose of a hydraulic seal?

Answer 7

used to prevent fluid from passing a certain point and keeping air and dirt out of the system

Question 8

why are seals not standardised ?

Answer 8

as not one type of seal is satisfactory for all installations;
- pressure at which the system operates
- the type of fluid used in the systems
- the metal finish and clearance between adjacent parts
- the type of motion in which it is fitted

Question 9

what are the three main classes that seals are divided into ?

Answer 9

• packings
• gaskets
• wipers

Question 10

what is it called when hydrauic seals are used internally on a sliding or moving assembly ?

Answer 10

packing seals

Question 11

when is it called when hydraulic seals are used between non moving fittings and bosses ?

Answer 11

gaskets

Question 12

what are V-rings?

Answer 12

one-way seals installed with the open end of the V facing pressure

Question 13

why must V-rings be correctly torqued?

Answer 13

otherwise it may not give satisfactory service

Question 14

what is a U-ring?

Answer 14

seals pressure in only one direction and must face the pressure. primarily used in low pressure systems

Question 15

what is the most common type of hydraulic seal?

Answer 15

an O-ring

Question 16

what type of hydraulic seal provides an efficient seal in both directions?

Answer 16

O-ring

Question 17

how can the use of an O-ring be identified ?

Answer 17

colour coding, however it is not reliable or complete means of identification
part number is more commonly used

Question 18

where are backup rings used?

Answer 18

where a high differential pressure is present, as a simgke seal might not be strong enough by itself

Question 19

where are static seals used?

Answer 19

to seal against steady or pulsating pressure

Question 20

where are dynamic seals used?

Answer 20

to seal where a stroking or rotational movements are present

Question 21

what are gaskets and where are they used?

Answer 21

static seals between two flat surfaces

Question 22

what should be avoided when installing or removing an O-ring?

Answer 22

using sharp edged tools

Question 23

what should be done to an O-ring when refitting or installing an O-ring in a hydraulic system ?

Answer 23

it should be immersed in hydraulic fluid first