×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

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

Jobs

Pump no flow protection.

Pump no flow protection.

Pump no flow protection.

(OP)
I have an application where i need to detect no flow or a dead end condition. As the heat builds up in the pumped fluid could give rise to an explosion, so iam told.
 The fluid is liquid fertilizer and quite corrosive, pipe size 6inch stainlesss steel flow rate 1000l/min.

Iam looking for instruments to use.
1. Paddle switch probably not last long as imersed in fluid.
2. Thermal dispersion needs to be wet all time
3. Mag flow very expensive.
4. Current, amps only change by 2%

Any suggestions please also what about looking at this from a temperature point of view.

RE: Pump no flow protection.

Some options might include ultrasonic clamp on systems.
From the temperature approach I would suspect a differential switch that will alarm when the difference between the temperature in the fluid affected by the pump is significantly higher than a reference temperature elsewhere in the fluid.
Another option might be a pressure switch or a differential pressure switch.
By switch, mechanical switch or trip-amp.

JMW
www.ViscoAnalyser.com

RE: Pump no flow protection.

(OP)
Thanks for the ideas,

1.Ultrasonic is too expensive to the client as they start around £500.00 mark.
2.Temperature difference is hard as only short run from suction to discharge is 8mts.
3.Pressure not sure as pump is mounted on surface then self primes from tank underground into vessel 3mtrs above ground so no delivery pressure to read.

Also no no return valve so pump has to self prime every start.


RE: Pump no flow protection.

If the stuff is going to blow up if you dead-head the pump, £500.00 is a small price to pay.  

You can just install a small recirculation (2 inch?) line from the outlet of the pump back to the tank from which the pump draws.  Put a manually adjustable throttling (globe) valve in the line. Set the flow for the minimum required  and padlock the handle of the valve in that position.

This way it will ensure that there is always enough flow to protect the pump, even if there would be no flow otherwise.  

RE: Pump no flow protection.

If the concern is 'dead-ending' the pump, pressure switch is installed on the discharge of the pump.

Another option for flow is external (clamp-on) ultra-sonic meter. No wetted parts with this one.

Is this a mag drive pump or canned pump due to the corrosive nature of the product?

Canned pumps can have temperature elements built into them.  These are quite helpful.

______________________________________________________________________________
This is normally the space where people post something insightful.

RE: Pump no flow protection.

Vote with JimCasey, A 1-1/2" line with a union orifice is what the Dr ordered.

RE: Pump no flow protection.

I guess the cost of protection always looks greater before an "excursion" than afterwards.
I always thought the only two ways to beat the bean counters were Health and Safety reasons or Environmental reasons.

JMW
www.ViscoAnalyser.com

RE: Pump no flow protection.

6" mag meter to expensive for a potentially catastrophic application? Don't you just love bean counters?

RE: Pump no flow protection.

Why would you not just temp sense the restrictions and pump points. Cheap, reliable, and to the point. (temperature!)

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Pump no flow protection.

Motor current may not change much. But motor power usually does since the power factor changes from something like .8 to less than .6 when 'dead-ending' (good expression that I just learned, thanks to controlnovice).

There are little relay-like devices that certainly cost less than GBP 500 that supervise power factor and can be used. You may need to install a current transformer (CT) if you do not have it already.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Pump no flow protection.

>>I guess the cost of protection always looks greater before an "excursion" than afterwards.
I always thought the only two ways to beat the bean counters were Health and Safety reasons or Environmental reasons. <<

The politicians always say the money is for the "chirruns", which apparently is pol-speak for the youth of our population.  

RE: Pump no flow protection.

dead-ending??  I have heard on the term "dead-heading".  As in pressure head.

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Pump no flow protection.

Dead-heading brings thoughts about the French revolution and madame Guillotine. Dead-ending is clear enough for me - and less bloody.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Pump no flow protection.

Operating a pump against a closed valve or with no forward flow is known as 'dead-heading' in the UK.

Aside for Gunnar: What was wrong with the guillotine? A little more care on choosing whose head goes in and it could be a great machine. Crying out for some automation though! surprise
 

----------------------------------
  Sometimes I only open my mouth to swap feet...

RE: Pump no flow protection.

Careful now, you limey!

I do not mind frog-eaters.

Gunnar, the rotten-herring-eater.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Pump no flow protection.

Gunnar, You're just going to have to enjoy your rotten herring on your own.  

The US Food & Drug Agency prohibits the import of surströmming, so we in the US are denied that malodorous experience.

Dan

RE: Pump no flow protection.

Don't forget! There's one snaps with each herring!
What about durian? Does FDA allow that?

Shouldn't this be red-flagged? It is awfully off-topic now. Isn't it?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Pump no flow protection.

"Dead Heading" is how I refer to it as well.

I used "dead ending" as it came from the OP.

______________________________________________________________________________
This is normally the space where people post something insightful.

RE: Pump no flow protection.

Oh, not "dead herring"?
Sorry, I wasn't paying attention.

JMW
www.ViscoAnalyser.com

RE: Pump no flow protection.

Red herring?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Pump no flow protection.

Gunnar, your command of idiomatic English is amazing.

I can't answer for the status of durian.  My food importer friend is a 'Lars' by name and deals only with that which the Swedish expatriate community craves: Vasa bread, Kalles kaviar and the like.

Dan

RE: Pump no flow protection.

I think with the information provided, I would prefer to opt for temperature detection, since this is the direct problem that is to be avoided.
A further problem that I noticed is that the pump self primes every time. If doesn't, then it will also get hot, but outlet pressure will be low.
The most simple way of avoiding the problem, instead of detecting it, is the one that has already been suggested twice: make a small bypass from the pressure side back to the underground tank.

RE: Pump no flow protection.

Dan,
I think he should bring in some Leksands Brungräddat and also some Vikabröd. They are really something, if you are into rye crisp.

Dave,
That bypass needs to be more than "small" if it shall have any effect. Can you justify the extra energy losses?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Pump no flow protection.

The usual way would be to control the by-pass with a pressure relief valve and he energy associated with operating this would be irrelevant to the pumps normal operation.
The pressure relief valve would be set to operate if the pressure exceeded the pressure when the pump is delivering into the open ended system. This is normally done to protect the pump and this approach presumes the pump was not supplied with an internal bypass.
From what has been said, that wouldn't be appropriate anyway since local internal circulation would probably also generate excess heating in the small amount of fluid being recirculated.
So: in this case an external bypass that feeds back to the tank would be necessary.
This means installing a T and some return pipe work with a pressure relief valve. I suspect that this would be more expensive than simply installing one of the sensor options and using them to shut down the pump.
Once tripped, the problem will disappear and thus you might need to latch the switch off until the cause has been investigated and it is safe to restart the pump.
Much depends on how troublesome it is to break into the pipeline to install various of the sensor options and hence the ultrasonic flow switch might prove a useful alternative.
One assumes that once you propose breaking into the pipeline  sensor costs may be the least of the costs if you have to do a Haz-Op review and if the installation is going to be expensive whatever the sensor chosen.

JMW
www.ViscoAnalyser.com

RE: Pump no flow protection.

Temperature sensors can easily be mounted outside pipe/pump. Surface temperature rises almost as fast as internal temperature.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Pump no flow protection.

//Can you justify the extra energy losses? //
In a way, I think so.
If we consider a 30kW pump, then roughly speaking, it would heat 1L of water by 7C per second. So if the bypass is 1L/s, then I suppose that the temperature rise is not dangerous.
A 30kW pump can pump roughly 750L/s over a 5m head. So the efficiency loss is quite small (1 in 750).

That is, assuming my scrap of paper calcs are not full of holes.

RE: Pump no flow protection.

I don't like temperature sensors for this application.  With the associated time delay, mostly they tell you that the pump got hot, not that the pump is about to get hot.  Since the stuff in these pumps is explosive, if you live lone enough to get a HI temp alarm,...RUN!.

That's why I proposed a completely passive strategy to ensure pump cooling; and always-on bypass line.  Sure it is not as energy efficient as some other scenarios, but it has no moving parts and can't fail.  

RE: Pump no flow protection.

I'd run open loop and temp sensors.

If the product isn't being in actively pumped to the 'user' then it's being fully or majorly bypassed back to the tank.

An 'always on' bypass can still be subject to heating when it clogs, or the drunk operator passes out and the whole unmonitored tank starts to heat up. (stretching?)

Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com

RE: Pump no flow protection.

Jim's idea of making the process self-protecting when all elements are behaving normally is a good idea. On a hazardous process I would expect at least one backup layer of protection to cover contingencies, and a temperature measurement with a tripping function designed to take the process to a safe state seems a reasonable second layer protection. Most temperature loops can be configured to give a digital output signal on a sensor fault which allows the control system to either warn the operator or automatically initiate an orderly shutdown on loss of the protection system. In Europe the current industry 'best practice' would be to carry out a SIL study on the protective elements in a hazardous process.
 

----------------------------------
  Sometimes I only open my mouth to swap feet...

RE: Pump no flow protection.

Thanks for embellishing, guys.  I certainly have no reservations about temp sensors except as a single and primary fault protection.  Normally I'm resistant to suggest a continuous bypass because of the waste in energy , but with a dangerous fluid as this has been described it is prudent to have a totally passive protection system.  Additional active systems such as temp monitors only contribute to additional safety.  

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!


Resources