Pumps

Pumps-Centrifugal -Shammi Apurva1Pumps-DefinationPumps are the mechanical devices which rotates and reciprocates to move fluid from one point to another i.e from low elevation to high elevation,low pressure area to high purpose area. Types Of PumpsDynamic Pump(Centrifugal).Positive Displacement Pump.

Dynamic Pump: Dynamic (kinetic) pumps such as centrifugal pumps in which energy is imparted to the pumped liquid by means of a moving impeller or propeller rotating on a shaft.The kinetic energy imparted to the fluid in terms of velocity by moving impeller is converted ton pressure as the liquid leaves the impeller and moves through a stationary volute or diffuser casing.Positive Displacement Pump: Positive-displacement pumps are those pumps in which energy is imparted to liquid in a fixed displacement volume such as a casing or cylinder by the rotating motion of gears, screw or vanes,by reciprocating pistons or by plunger. Major drawback of positive displacement is that it cant operate against closed valve on discharge side of pump,as it doesnt have shut off head as that in centrifugal pump.# In this presentation we will consider the dynamic pumps,their parts and Selection procedures.

Centrifugal PumpRotating and stationary components

Classification of Centrifugal PumpCentrifugal Pump are further classified into 3 categories as per API-610:

Overhung PumpBetween Bearing PumpsVertically Suspended Pumps

Generally, Overhung Pump are used in different process as it is small in size ,least expensive & is most efficient.

Between Bearing Pumps are used where the heads are very high. They are further classified as on the basis of stages and split (Axial and Radial Split)Radial Split are taken into consideration on following measures:1.Pumping temperature of 200 C (400 F) .2. Liquids with a relative density of less than 0,7 at the specified pumping temperature.3. Liquids at a rated discharge gauge pressure above 10 MPa (100 bar; 1 450 psi).

Vertical Pumps are mainly used where sump is present or is placed in tank .Overhung PumpVertical Inline Horizontal

Between Bearing Pumps

Radial Split Axial Split

ImpellarsAn impeller (or impellar) is a rotor inside a tube or conduit used to increase (or decrease in case of turbines) the pressure and flow of a fluid. An impeller is a rotating component of a centrifugal pump, usually made of iron, steel, bronze, brass, aluminum or plastic, which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the center of rotation.

Types Of Impellar:Open ImpellarEnclosed ImpellarSemi-Open Impellar

Impellar-Types

Open ImpellarEnclosed ImpellarSemi-Open ImpellarOpen Impellar: Simple in design and low costDisadvantage:distortion,efficienc is low,structural weakness.Enclosed Impellar: This impellar are generally used in pump handling clear liquid to save from back flow we will provide thrust bearing.Semi-Open : This type of impellar are easy to manufacture,efficiency is high.

#lower disc friction and tighter axial clearances-Works more efficiently than other impellar,accessible for applying surface hardening treatments & easy to manufacture.

Types Of FlowAxial Flow:

Radial Flow:

Mixed Flow:

Selection Criteria -PumpSelection of process pumps can be mainly divided on the basis of liquid characteristics as well as on other following conditions:

1.Pump for viscous liquids-2.Pump for clear liquids- 3.Pump for low flow- 4.Pump for corrosive liquids5.Pump for slurry6.Pumps for specific Service7.Pump for high pressure service8.Pump for low energy9.Pump for low maintenance cost10.Pump with high standard of safety in operations11.Pump for specific speed

Certain points to be considered during pump selection are:Fluid Characteristics: In this, we generally go along the service name of fluid for which pumps are designed.Under this,Chemical identity of fluid also comes such as corrosive ,toxic etc.Specific Gravity: It is the ratio of weight of a given volume of solid/liquid to that of an equal volume of water .Viscosity: It is the property of a liquid which resists the flow of the liquid (opposite of fluidity).Viscosity decreases with rise in temperature.Temperature:Lubricating quality of liquid handled:Space available for pump:System head

Pump DesignThe design of pump covers the various engineering activities related to parameters,which are required to perform pump calculation.The following parameters are to be considered:1.Flow Rate.2.Head Requirement.3.NPSH available.4.Design pressure and temperature.5.Power Requirements.6.Driver Type7.Hazards Caused by fluid properties such as flammability,toxicity and corrosivity.8.Fluid Status eg. Solid Contents, Dissolved gases.9.Material Of Construction.10.Number Of Installed Pumps. (number in service + number of spares).

NPSHNet Positive Suction Head: The pressure required at the suction of pressure to prevent cavitation. Here,positve means above zero. The Net Positive Suction head is an important factor in the design of pumps and distinction must be made between: The NPSH available(NPSHa) in a pumping service determined by the process designer. The NPSH required (NPSHr) of the selected pump as specified by the pump vendor.NPSH is closly related to cavitation .Cavitation is basically the formation of bubbles due to low pressure area and subsequently collapses upon migration to a high pressure area.NPSHa: NPSHa stands for Net Positive Suction Head available.It is the net remaining pressure at the suction flange of the pump after subtracting all negative forces that restrict liquid from getting into the pump.NPSHa is the pump characteristics,provided by process engineer.NPSHr: A similar term NPSHr is used by pump manufactures to describe the energy losses that occur within many pumps as the fluid volume is allowed to expand within the pump body. This energy loss is expressed as a head of fluid.NPSHr values are given by vendors based on their pump models.

Formulas used:

NPSHa : (Pe +Pb Pd)/ * g .( MDS-Mechancial Datasheets)

NPSHr = (as per PUMP PDS-Pump Datasheets)

A = 7.2 for double suction and 3.6 for single suction pumps Note:The difference between NPSHa to NPSHr is 1.5 and 1.3.

Cavitation: Formation of bubbles due to low pressure area and subsequently collapses on migration to high pressure area. It causes vibration in pumps.

Head loss: In practical term it is considered that head loss take place per 100m of straight pipe. Hv = .v2/2g.

Accessories of PumpsCouplings: Couplings join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both.FUNCTIONS OF COUPLINGS: Flexible couplings join two pieces of rotating equipment while permitting some degree of misalignment or end movement or both. The three basic functions of a flexible coupling are to :1. Transmit power2. Accommodate misalignment3. Compensate for end movementTypes Of Couplings:1.Mechanical element2.Elastomeric element3.Metallic element

Mechanical Seals: The mechanical seal is a device that forms a barrier between rotary and stationary parts in the pump. The seal must block leakage at three points:1. Between the faces (rotary and stationary) of the seal.2. Between the stationary element and the seal chamber housing of the pump.3. Between the rotary element and the shaft or sleeve of the pump.These basic components and functions are common to all seals. The form, style, and design vary depending on the service and the manufacturer.

Seal System Categories:

Category 1: Seals used in non-ISO/ API pumps, i.e. preferably meeting the dimensional requirements of ASME B73.1, ASME B73.2 and ISO 3069.Temp. Range - -40C to 260C Absolute Pressure Up to 22 bar

Category 2: Seals used in ISO/ API pumps that preferably meets the dimensional requirements.Temp. Range - -40C to 400C Absolute Pressure Up to 42 bar

Category 3: Seals used in ISO/ API pumps that preferably meets the dimensional requirements. But requires rigorous testing and documentation.Temp. Range - -40C to 400C Absolute Pressure Up to 42 bar

Seal System Types:

Type A: Seal is a balanced, inside-mounted, cartridge design, pusher seal with multiple springs and in which the flexible element normally rotates. Secondary sealing elements are elastomeric O-rings. Type B: Seal is a balanced, inside-mounted, cartridge design, non-pusher (metal bellows) seal in which the flexible element normally rotates. Secondary sealing elements are elastomeric O-rings. A metal bellows seal offers the advantage of having only static secondary seals. It may be specified instead of the standard Type A seal for low temperature service.Type A and Type B seals are suitable for temperatures up to 176C.Type C: Seal is a balanced, inside-mounted, cartridge-design non-pusher (metal bellows) seal in which the flexible element is normally stationary. Secondary sealing elements are flexible graphite.Bellows seals are inherently balanced. Stationary metal bellows seals are the primary choice for high temperature service. Type C seals are for high temperatures up to 400C.

Seal System Arrangements:

Arrangement 1: Seal configurations having one seal per cartridge assembly.

Arrangement 2: Seal configuration having two seals per cartridge assembly, with the space between the seals at a pressure less than the seal chamber pressure.

Arrangement 3: Seal configurations having two seals per cartridge assembly, utilizing an externally supplied barrier fluid at a pressure greater than the seal chamber pressure.

The principal difference between Arrangement 2 and Arrangement 3 configurations is the concept of containment of leakage versus the elimination of process fluid leakage.

Different Seal PlansMechanical Seal Plans:

Plan 11Plan 13Plan 21Plan 23Plan 31Plan 52Plan 53 APlan 53 BPlan 62For furthur reference regarding mechanical seals and their application visit the websites : www.flowserve.com and API 682.

Pump Control SystemPump control system lie from single hand operated valve to highly automated valve . For centrifugal pump , either change of speed or change of valve setting can control the desired variable.

Pump Operation

Series Operation- For Head

Parallel Operation-For Flow

24Power Consumption Pump Power Input: It is mechanical energy at the pump coupling or pump shaft absorbed from the device. P= Q.g.H./ 1000. in kW. Or Q.g.H./ 367. in kw where q in m3/hr

Drive Rating: It is general consideration that during operation flow and operating point fluctuates which increases the power consumption of pump,so for that following safety margins are used for determining the motor size. upto 7.5 kw approx.20% upto 40 kw approx.15% upto 40 kw approx.10%If extreme flow fluctuations are expected ,the motor size must be selected with reference to the maximum possible pump capacity on curves,taking into consideration: Impellar diameter required,Condition NPShaNPShr,permissible P/n values for bearings.Changing the SpeedTrimming the ImpellerChanging the Speed: The same pump has different curves for different speeds;these curves are interconnected by the similarity law i.e affinity law. Q N H N2 P N3 Trimming of Impellers: Impellers are trimmed when excess flow rate are available, Pump operating far from its design point ,Operating head and flow rate are greater than process. So,to permanently reduce the output of centrifugal pump operating at constant speed impeller diameter D is reduced. (D1/D2)2= Q1/Q2 =H1/H2Changing the Pump Performance