Questions

12.1 Isolation Valves - Linear Movement

1 What is the main advantage of a gate valve?
a) They are better than all the other linear movement valves for producing a tight shut-off on steam systems
b) They can be used in throttling applications as well as for isolation
c) There is a low pressure drop across the valve
d) They are easily automated
2 In which of the following applications should an outside, non-rising stem be used?
a) Where a gland packed valve is used in a corrosive fluid
b) Where a bellows sealed valve is used in a steam system
c) Where there are no temperature variations of the fluid passing through the valve
d) Where a bellows sealed valve is used in a corrosive fluid
3 Why must balancing plugs be used in globe valves that are larger than DN250?
a) The pre-lifting plug enables more precise control of the fluid
b) It reduces the pressure drop across the valve allowing the valve to open easily
c) It allows the valve to be balanced on water circuits
d) A balancing plug has to be used with a bellows seal
4 What is the main reason for choosing a bellows sealed stem over a gland packed one?
a) A bellows seal will never require maintenance
b) The bellows seal produces a ‘zero emissions’ seal
c) Gland packed seals on valves above DN250 are prone to leakage
d) All of the above
5 Which of the following valves should be used where the valve is to be welded into a pipeline and rapid seat wear is expected?
a) A globe valve
b) A parallel-side valve
c) A diaphragm valve
d) A piston valve
6 Why is a diaphragm valve not suitable for most steam applications?
a) Condensate collects in the weir, increasing the pressure drop across the valve
b) Diaphragm valves are incapable of producing a tight shut-off above 4.0 bar
c) The diaphragm valve is only suitable for handling fluids containing suspended solids
d) Diaphragm materials are not suitable for temperatures above 175°C