Oil becomes black

(1) Alagappan Coating inside the bearing... October 8th, 2007, 05:30 PM

(2) pumps100 Sorry but I don't think any... October 31st, 2007, 01:12 PM

(3) S. L. Abhyankar Dear Mr. Alagappan, To my... November 6th, 2007, 06:57 AM

(4) Alagappan Dear Mr.Abhyankar/... November 6th, 2007, 06:20 PM

(1) Dear all,

Please suggest based on your experience relevant coating to be used inside the bearing housing(oil sump) in order to prevent oil get balckened(change of colour) during operation. The material of the bearing housing is cast steel and oil used in the sump is ISO VG 46. The temp. may go upto 150 degree celcius.

Thanks in advance for the suggestions.

(2) Sorry but I don't think any coating system of your bearing housing is appropriate regarding your perceived 'problem' with the oil going black.

You don't say if you are having a problem with the bearings. Most lubricating oil will discolour after being put to work.

If you change the oil just because of its appearance (being black or discoloured) this is a mistake. What I would suggest is that you invest in getting the oil analysed next time you change it. This will tell you the condition of the oil and also give you an idea of what service intervals you really need.

However, if you do find that the bearing life is being affected by degradation of the oil quality, due to particulants/sediment build-up, and/or high temperature, you need to talk to the bearing and lubricant supplier to offer you a solution. This might involve a change in the oil type used, filtration, cooling, or simply a different maintainance regime.

Regards

John

(3) Dear Mr. Alagappan,

To my mind, surface of the oil reservoir has nothing to do with oil becoming black. Oil becomes black, due to wear of the bearings and due to carbonization of components of oil, especially when working at high temperature. In fact instead of worrying about oil becoming black, it should be used as the indicator to judge when to change the oil.

Regards,
S. L. Abhyankar

(4) Dear Mr.Abhyankar/ Mr.John,

Thanks for your valid suggestions.

Alagappan.E

Pump Curves change

(1) ethanhan Re: Pump curve March 8th, 2008, 01:49 PM

(2) S. L. Abhyankar Dear Mr. Ethanan, Pump... March 22, 2008, 05:47 PM

(1) hi to all

Do pump curve change when type of liquid is different? Yes I am mentioning a same type of pump.

Thanks

ethanhan

(2) Dear Mr. Ethanan,

Pump Curves is a generic term. Within that generic nature, there are four curves - H v/s Q, Input power required v/s Q, Efficiency v/s Q and NPSHr v/s Q.

These curves change due to 5 reasons - Speed, diameter, density of fluid Vapour pressure and viscosity. Most complex of these is change in viscosity, because it affects all parameters - H, Q, Efficiency (and in turn) Power.

As you have yourself rightly pointed out, one has to be systematic and cautious to use in Head as meters of liquid column. One must convert the values in pressure units to Head in meters of liquid column.

Hope, this clarifies.

Thanks,
S. L. Abhyankar

Rated and Nominal Duties

(1) rainman Pump Rated Conditions March 14th, 2008, 12:08 AM

(2) S. L. Abhyankar Dear "Rainman", By... March 17th, 2008, 06:38 PM

(3) rainman ---------------------- Abhyank... March 17th, 2008, 09:56 PM

(1) Pump Rated Conditions

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For centrifugal pumps, what do the term “rated” parameters (flow, NPSHr, etc.) mean? How do the pump manufacturers determine these values? Are these values specified by the customer or the pump manufacturer? My questions arise because I wonder if my rated flow for any particular pump should change when the normal flow for this pump is changed, as a result of a new condition being implemented in the plant where it is used (say a revamp). To illustrate my point further, I have a pump originally designed to handle a normal flow of 50 m3/h and for which a “rated” flow of 56 m3/h, was defined, according to the information provided in the pumps data sheets for the original project. After some years, a revamp of the plant is under way, which requires a new normal flow of 53 m3/h. Under these circumstances, will I have a “new” rated flow also, if the pump and the hydraulic (curve) system remain the same? What if I change my system (by increasing, for instance, some pipe diameters)?

Thank you all in advance for your feedback,

Rainman

(2) Dear "Rainman",

By my understanding of the terms "Rated Duty" and "Normal Duty", Rated Duty would be the duty on the nameplate of the pump, printed by the manufacturer, declaring the pump's compliance with the duty mentioned in the order from the buyer. "Nominal Duty" would either be

i) the duty at the point of best efficiency (BEP) or

ii) If it is a pump supplied as per a standard, such as ISO-2858, there are "Nominal" duties or ratings specified in the standard

Coming to your point about changes that may happen in the performance of the pump, or change needed in the performance of a pump during revamp, the duty obtainable from a pump is the point of intersection of the system curve with the pump's curve. For example, if you change the system, using larger pipe sizes, as mentioned by you, the system curve would become one with less friction. So, one would get more discharge from the pump. Whereas less friction and higher flow would mean better performance of the pump, at higher flow the driver may get overloaded. So, one needs to also check the power requirement of the pump at the changed duty.

I hope, I have touched most of the points raised by you.

S. L. Abhyankar

(3) Abhyankar,

Thank you for your kind answer, it confirms some of the feelings that I had about this issue; inasmuch, as I sort of had a little argument about it with some other people. I believe one of the purposes of this forum is to open discussions on any issue, no matter how simple or trivial this may sound, in order to get the opinions, feedback or answers in a polite and simple way, without offending, like some people on this forum do.

Rainman

Why Pumps have Vent and drain?

(1) ethanhan Vent and drain 20 March 2008, 05:41 PM

(2) pumps100 (John) Dear Ethanhan, I think you... 20th March 2008, 06:31 PM

(3) S. L. Abhyankar Vent and Drain are also... 21st March 2008, 04:50 PM

(1) To all experts

Why vent and drain are needed in pump??? probably where is it located?

Thanks(especially John)

Hor Win Han (Ethanan)

(2)

Dear Ethanhan,

I think you are referring to vent and drain connections pursuant to API 610 sealing plans. Can I ask that for future queries if the query relates to API pumps please say so.

I will assume that your query relates to API610. I must confess that I don’t have that much experience in relation to centrifugal pumps used in the petroleum, petrochemical and natural gas industry; but I will try my best to answer your query.

Within API 610 there are a number of shaft sealing plans which I believe cross relate to API 682 Shaft sealing systems for centrifugal and rotary pumps. See also ISO 21049.

The standards will provide for a number of tappings (normally half inch NPT I think?) in the seal chamber on the API 610 pumps. These tappings may be used, or not used, dependent on the pumping application. These are normally located in the seal chamber.

The vent and drain connection – sometimes also called the quench connection can be used for a number of purposes. For example suppose you were pumping some really thick stuff like bitumen or tar you could introduce low pressure steam to stop the ‘liquid’ solidifying on the shaft/mech seal when the pump was stopped or when the liquid cooled down to ambient temperature.

You could also use the tapping to use a water flush to take away any leakage from the seal area. In the event of a seal failure (if a double mech seal was used) the ‘vent’ could take away this liquid – this is handy for example if you were pumping something nasty like acid or other highly corrosive or toxic liquids.

But please look at API 610 and API 682 for further guidance as I am no expert in this field.

Regards

John

(3)

Dear Mr. Hor Win Han,

Vent and Drain are also provided on most volute casings of centrifugal pumps.

The vent connection is to release any air or gases likely to get entrapped in the casing, which is always a possibility especially with split casing pumps and end-suction pumps with side discharge volute.

Drain connection is of course at the bottom-most portion to drain, better still, flush and drain any settle-able foreign matter entraining in the flow or material disintegrating due to corrosion or abrasion.

The drain connection will be of fairly large size in case of solids-handling pumps, such as paper stock pumps.

Hygienic pumps, such as pumps in dairies need flushing at regular intervals. So, instead of a simple drain connection, the pumps are provided with quick clamping and unclamping feature.

Hope, this clarifies your query.

S. L. Abhyankar

Would over-rated motor damage pump-screw?

Q – What role would moment of inertia of the motor play in damaging, rather, shearing the power screw of a triple screw pump? Salient details are –

1. Pumped liquid – lubricating oil
2. Capacity 160 lpm
3. Rated pressure – 180 bar
4. Drive – 60 kW, 2900 rpm
5. Mounting – Vertically into a 36 m³ oil tank. Minimum submergence recommended to avoid vortex-formation, air entrainment, dry running is 40 mm. The recommendation is not always followed.
6. Constructional features – There is no packed gland or mechanical seal. Pump shaft or the power screw has a balance piston on the driver side, with close clearance between balance piston and pump casing. Leakage if any, maximum 0.5 lpm, would flow over the pump and drip back into the oil tank.
7. Material strength and diameter of power screw – 24mm, 16CrMnS5, with minimum UTS of 570 MPa

by C. S. Cowlagi, anucool16@rediffmail.com

Answer – To get a clarity for myself, on the role of moment of inertia of the motor, I would paraphrase the question a little differently. “Though a pump requires only 60 kW motor, would a 100 kW motor, inadvertently or even wantonly connected, cause damage, rather shearing of the pump shaft?” My logical answer would be “No”.

A 100 kW motor would have much higher moment of inertia than a 60 kW motor. If the shaft has suffered seizure, a 100 kW motor has rather, a better chance of overcoming the seizure and make it run than a 60 kW motor.

The root cause of the failure seems to be the seizure of the shaft than excessive moment or torque imparted by the motor.

Standards for motors specify pull-up or starting or locked rotor or breakaway torque to be 150 percent of full-load torque. This testing is typically done by locking the rotor. This actually simulates a seized shaft and demonstrates capacity of the motor to overcome seizure.  A motor does try to overcome a seizure. Excessive torque may get imparted in this effort of the motor to overcome the seizure. But the demand for excessive torque comes from a seized shaft. If the shaft is not seized and does not demand any exccssive torque, the motor will not impart, by its own volition, any torque more than what the driven shaft demands. If the driven shaft demands only 10 kW load from a 60 kW motor, the motor would provide just as much. That is what is called as part-load running of the motor. Efficiency of the motor would of course be poor in such part-load running. Motors have power demand of their own, even when running on no load or zero load. So, motors can run all the way from zero load or no load to full load and somewhat beyond full load, which is overload. Basic fact is that motors respond to the demand. They do not impose load on to the driven equipment. They impose load on to the supply system, not on the driven system.

Root causes of the shear of a driven shaft would be misalignment, thermal load, seizure. Possible causes for a shaft of a screw pump to suffer seizure would be dry running.

 

Incidentally, if both the power screw and the idler screw have same metallurgy and are, of course, running in frictional contact, they are susceptible to suffer electrolytic galling and consequently a seizure, more so in dry running.

 

To prevent dry running in the given installation, it seems that a level controlled interface with the motor’s starter would be a good protection. The other check should be on using dissimilar metallurgies to avoid electrolytic galling at surfaces in frictional contact.