11.11 Perssure Control Flashcards
why are relief valves used in a hydraulic system?
to ensure a safe constant predeturmined maximum pressure in a system
what are the most common types of pressure relief valves in a hydraulic system ?
-ball type
-sleeve type
-poppet type
when a pressure relief valve is incorperated as a system relief valve what is this for ?
as a safety device incase of a failure in the pump or other pressure regulating devices
when a pressure relief valve is incorperated as a thermal relief valve what is this for ?
used to reliefe excessive pressure due to thermal expansion of the fluid.
what is a thermal relief valve usually used in conjunction with?
when a check valve or a selector valve prevents pressure from being relieved throughthe main pressure relief valve
what is the purpose of a pressure regulator?
to manage the output of the pump to maintain system operating pressure. and to permit the pump to turn without resistance
what is the purpose of a hydraulic seal?
used to prevent fluid from passing a certain point and keeping air and dirt out of the system
why are seals not standardised ?
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
what are the three main classes that seals are divided into ?
- packings
- gaskets
- wipers
what is it called when hydrauic seals are used internally on a sliding or moving assembly ?
packing seals
when is it called when hydraulic seals are used between non moving fittings and bosses ?
gaskets
what are V-rings?
one-way seals installed with the open end of the V facing pressure
why must V-rings be correctly torqued?
otherwise it may not give satisfactory service
what is a U-ring?
seals pressure in only one direction and must face the pressure. primarily used in low pressure systems
what is the most common type of hydraulic seal?
an O-ring
what type of hydraulic seal provides an efficient seal in both directions?
O-ring
how can the use of an O-ring be identified ?
colour coding, however it is not reliable or complete means of identification
part number is more commonly used
where are backup rings used?
where a high differential pressure is present, as a simgke seal might not be strong enough by itself
where are static seals used?
to seal against steady or pulsating pressure
where are dynamic seals used?
to seal where a stroking or rotational movements are present
what are gaskets and where are they used?
static seals between two flat surfaces
what should be avoided when installing or removing an O-ring?
using sharp edged tools
what should be done to an O-ring when refitting or installing an O-ring in a hydraulic system ?
it should be immersed in hydraulic fluid first
