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Displacer level switch VS. float level switch
Can I change displacer level switch with float level switch?

Dear experts,
I've been to an oily water treatment plant where they put all drains (Oil & Gas plant) in a sump and then treat these drains until it's ready to be thrown into the sea.

They have displacer level switches which control sequence of pumps.
The point is that these displacer switches suffer from corrosion (H2S gas), the displacer switches are Magnetrol and I know it's one of the best Manufacturers around the world.

They lose displacer spring every now and then and they have to change the whole displacer switch.

Is it possible to use float level switch (Cable) instead of displacer (Spring) in this application?

How can I decide either to use displacer level switch or float level switch in any application?

You're right, Magnetrol switches do work well in that application. You could substitute a ball float type such as Flygt ENM10 however they also have issues especially if you have number of them in the same sump.

Have you spoken to Magnetrol? I'm sure they have lots of experience with H2S atmosphere. Perhaps you could fit a rubber boot around the cable exit or purge with air.

Roy

1) I hope you are talking about the cable type float level switch in which you intend to keep both the switches as well as the magnet inside the measurement medium. If it is the case Yes, you can use a cable type - float level switch instead of the displacer type level switch. But off course there are some matters to be taken care of,

First of all a float material selection is important. Float material should not react with your medium of measurement / measurement medium should not be corrosive to the float.
Second is the material selection of the cable insulation, the nature of medium comes in to picture.
Third is the turbulence in the sump. This can affect the measurement.

2) If you think about the float with rod placed on top of the float which is extended to top of the sump. Either the magnet is attached to the rod or the target part of the rod is made up of magnetic material. Switch is installed externally at the chamber. This type usually used for low range of liquid level. But you can opt for this option too. But here also the float selection comes in to picture.

3)Another option is to use a displacer type level transmitter (continuous level measurement) and you can generate the high / low level state using trip amplifiers / plc logics etc.

4)Best option for this type of corrosive environment is to use non-contact type level measurement. Like radar type, ultrasonic type etc. But this is costly; off course.

regards,
Rajeeb

1 out of 1 members thought this post was helpful...

When using equipment in a sour service (where H2S is present), corrosion is often an issue. Choosing materials compatible with sour service becomes critical. A simple way to ensure that the materials of construction of your level switch are compatible with sour service is to specify NACE construction. Otherwise, the materials must be looked at individually.

Displacer springs are usually Inconel 600, which, as you have discovered, is not particularly good for sour service. A better choice is Inconel X750.

Magnetrol offers NACE construction on top mounted displacer switches and that includes an X750 spring. This would likely solve your corrosion problem.

Top mounted displacer switches are ideal for sump applications for several reasons:
1) The flexible displacer cable can be made as long as necessary without concern of damage (such as might be the case with a rigid float stem).
2) Sumps tend to hold various liquids with varying densities. Displacer switches will function reliably over a wide range of densities.
3) Displacer switches can be set up with multiple switches in a variety of actuation configurations, so alarms and/or pump control can be achieved using displacer switches.

Regards,
Katie Hay
Buoyancy Product Manager
Magnetrol International, Inc.

Any suggestion for HRSG blow down pit level application?

By S, Elavazhagan on 13 November, 2009 - 4:50 am

Hi,

The Float level switch can be very well used since it is not a
pressurized pit. We have used in previous projects too.

With best regards,
S. Elavazhagan

Dear Sir,

What kind of level switch final you have used for H2S environment? We have the same condition on out plant. Please advise.

>I've been to an oily water treatment plant where they put
>all drains (Oil & Gas plant) in a sump and then treat these
>drains until it's ready to be thrown into the sea.
>
>They have displacer level switches which control sequence of
>pumps. The point is that these displacer switches suffer from
>corrosion (H2S gas), the displacer switches are Magnetrol
>and I know it's one of the best Manufacturers around the
>world.
>
>They lose displacer spring every now and then and they have
>to change the whole displacer switch.
>
>Is it possible to use float level switch (Cable) instead of
>displacer (Spring) in this application?
>
>How can I decide either to use displacer level switch or
>float level switch in any application?