4 replies to this topic

[Brenno]

Hi all,
I'd like to hear some thoughts on installing high point vents in piping to prevent airlocks and poor pumping performance during start-ups, when the pipework is initially full of air.
Is this a common practice? Is it necesary? Are there any alternatives?

[ankur2061]

Hi all,
I'd like to hear some thoughts on installing high point vents in piping to prevent airlocks and poor pumping performance during start-ups, when the pipework is initially full of air.
Is this a common practice? Is it necesary? Are there any alternatives?

Brenno,

High point vents are a necessity when the pipework is long and when any air coming in contact with the process is deleterious to the process (e.g. undesirable oxidation reactions due to trapped air).

High point vents may be temporary or permanent depending upon the commisioning plan envisaged for the plant/unit.

Temporary vents (also called commisioning vents) coud be connections provided at high points with flexible hose or hard pipe spools that can be easily dismantled after the system is vented and then blanked off with blind flanges.

Permanent vents should be provided if vapor locks are envisaged during normal operation of the pumping system.

Toxic/Volatile/Flammable liquids should not be vented to the atmosphere (open collection in a drain pan). If there is a venting requirement for such liquids the vent pipe(s) should be connected to a closed drain system.

Location of high point vent connections should be carefully evaluated during the detail engineering stage of the plant/unit in order to avoid goof-ups at the commissioning stage.

Hope this helps in getting an idea of high point vents.

Regards,
Ankur.

[Brenno]

Hi ankur,
Thanks a lot for your answer.
what i've been asked to do is install 2 vents on the highest points of 2 ctw lines.
When you say lines where vapor locking is expected to occur should be fitted with vents, what are the criteria under which lines are subject to vapor locking?

Would the pressure of the pump eventually expel air from the high points of the lines out to the receiving tank?

[ankur2061]

Hi ankur,
Thanks a lot for your answer.
what i've been asked to do is install 2 vents on the highest points of 2 ctw lines.
When you say lines where vapor locking is expected to occur should be fitted with vents, what are the criteria under which lines are subject to vapor locking?

Would the pressure of the pump eventually expel air from the high points of the lines out to the receiving tank?

Brenno,

Generally air locks form in liquid lines which are being commisioned for the first time or during a start-up after a long shutdown. Also air lock formation depends on the pipe routing, specially if the piping is having loops, sudden twists and turns and sudden elevation changes. Pipework having too many elbows/bends is also likely to have air lock fomation. Restriced use of elbows/bends, pipe expanders/reducers will help to reduce likeliihood of air locks.

Air locks can get expelled by the pressure of the pump into the receiving tank but it is also possible that they may not, which can cause line hammering and also restricted flow causing a general deterioration of the pumping system performance.

Hope this helps.

Regards,
Ankur.

[Whit123]

Hi ankur,
Thanks a lot for your answer.
what i've been asked to do is install 2 vents on the highest points of 2 ctw lines.
When you say lines where vapor locking is expected to occur should be fitted with vents, what are the criteria under which lines are subject to vapor locking?

Would the pressure of the pump eventually expel air from the high points of the lines out to the receiving tank?

You should also think of installing relief valves if your lines are long, with many bends and likely to result in pipe hammering. Since it is a water service you can vent them directly to the atmosphere.