Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Centrifugal pumps alarms and trips

Centrifugal pumps alarms and trips

Centrifugal pumps alarms and trips

Hello everyone

I was wondering if there is any standard or recommended practice regarding typical alarms and trips to be implemented around centrifugal pumps?

The reason is: in the refinery I am working in, I see plenty of alarms and trips that I don't see the purpose.

For exemple, on pumps (canned motor pumps coming with their own winding TSHH) discharging LPG from debutanisers (gasoline HDT and catalytic reformer) to deethaniser, we can see:

- PDAH on suction filters (OK)
- PAL on suction (OK)
- TAH on suction (redundant with PAL on suction?)
- FAL in discharge (OK)
- PAL on discharge (why?)

- LSLL on suction drums (OK)
- PSLL on suction (OK)
- TSHH on suction (redundant with PSLL?)
- PSLL on discharge (why?)
- FSHH on discharge (redundant with PSLL on discharge? but maybe a better option?)

On other pumps, I have also seen PDAL and PDSLL (between pump suction flange and suction drum) to trip the pump on low NPSHA (similar to PSLL on suction)...

So could you please let me know your thoughts on that (I have indicated my comments next to the above items)?

I do understand that alarms and trips are selected on a case by case basis, but maybe there is a minimum set to implement, but I don't know where to find this information.


@Lionel_Sheiko / geniechimiquefacile.com

RE: Centrifugal pumps alarms and trips

The vendors of the canned motor pumps should be able to give you a preferred configuration for pump protection and the reasons for each device.

It is my understanding that high-temperature operation poses the largest threat to canned motor pumps, with run-dry and bearing failure being the second largest threats

I would consider the purchase of a packaged protective device devices available for these pumps. There are many advantages of a continuous monitoring system



Sr. Process Engineer

RE: Centrifugal pumps alarms and trips

IMO, the redundant of the pump alarms and shutdowns may be resulted form the HAZOP, AOA, and SIL requirements. Typically as the level identified per risk assessment matrix, it requires certain number of the safety measures in place to mitigate the potential risk. The additional alarm or shutdown may be required to satisfy the risk level as identified.

RE: Centrifugal pumps alarms and trips

Check the hazop worksheets and / or with the pump vendor if the PSLL on pump discharge will pick up some serious abnormality within the pump that the FSHH wont.

RE: Centrifugal pumps alarms and trips

"Is there a standard practice" - Not really.

Most of those you've listed are though pretty standard, but it depends on the process, size of pump, fluid, design pressures and temperatures etc.

What you're trying to do is protect the pump from damage if it sees fluid conditions outside it's operating envelope. So for a pressurized high vapour pressure liquid like you have , this includes low pressure ( liquid will boil and you'll get vapour in a pump not designed for it) and high temp ( again potential gas or damage to pump) or no or low flow which long term could damage the pump.

Whether you need them all and what levels they are set at should be addressed in a LOPA study or alarms review. The alarms study looks at whether there is sufficient time and warning for the operator to actually do anything if the alarm goes off before the unit trips. In an upset condition the controller can become overwhelmed with alarms and so their usage needs to be curtailed to those that actually are useful. Trips on the other hand work well in extremis and if set at the correct level shouldn't inhibit the process.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: Centrifugal pumps alarms and trips


Discussing with the reliability guy, I have learnt that PAL and PSLL on discharge side aims at limiting flowrate above 10-20% of BEP. In fact, only PT were available on currect pumps when decision to install additionnal safety loops has been taken. So the choice to install PSLL instead of FSHH.

@Lionel_Sheiko / geniechimiquefacile.com

RE: Centrifugal pumps alarms and trips

Also, in many cases, a plant will adopt their own "standard" for protection logic of motors, pumps, etc. based on their own preferences (sometimes driven by HAZOP, internal lessons learned, or other considerations previously noted).

RE: Centrifugal pumps alarms and trips

As you've already identified there lots of things to monitor and protect pumps...

Our preference is always power monitoring (true power) so that as soon as process upset happens for whatever reason, then immediately the power will change and once limits are set to within the minimum and maximum flow limits, the motor will trip as soon as these flow-rates are reached - for more info follow the link http://www.cdrpumps.co.uk/pump-protection/

As rule of thumb, low flow should be ideally more than 20% of the flow at BEP and no more than 10% past BEP - of course there is always flexibility but generally follow these rules and you will be safe !

Ash Fenn


RE: Centrifugal pumps alarms and trips

And don't forget that since there is a high likelihood that all the machinery and piping is insured, insurance companies also have requirements. So check them out.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


White Paper - Effects of AIA Quick Guide to UL 489 or UL 1077
The function of a circuit breaker is to provide overload (thermal) and short-circuit (magnetic) protection to a circuit and its downstream components. A circuit breaker functions like an airbag in a car, protecting circuit components and people by tripping the circuit to interrupt the current flow if it detects a fault condition in the control system. Download Now
White Paper - Guide to Integrate Large-Format Additive
As with any new technology, getting into large-format 3D printing begins with investigation. The first question may be a simple one: what does “large-format” mean? For 3D printers, “large” is a relative term. Many extrusion-based (FFF) 3D printers are referred to as desktop machines, because they fit on table space. Some of these have very respectable build volumes – but when it comes to “large-format,” the machines will need their own dedicated floor space. Large-format 3D printers have significant build volumes and are most often found in professional settings, like manufacturing facilities and R&D centers. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close