Chemical Technology August 2015

Chemical Technology • August 2015

entire range of specified and anticipated viscosities and

pump shaft, coupling, and driver will be designed to

transmit highest torque associated with lowest pumping

temperature. Also, when a centrifugal pump is selected to

handle a viscous fluid, the engineer should ensure that

the vendor’s water performance curves are corrected for

head, capacity and efficiency.

• V:

A pump’s flange rating is governed by maximum allow-

able working pressure (MAWP). Engineers should verify

that flange rating is based on MAWP corrected for the

maximum pumping temperature and that the hydrostatic

test pressure is determined from the MAWP which is

corrected for temperature and material of construction

of the pump.

• W:

Axial thrust in pumps is yet another area to be aware of.

Axial loading is governed by differential pressure across

the faces of impeller(s). In the case of vertical pumps,

the weight of the rotor adds to down thrust. Pump out

vanes on the back of the impeller, balance holes and

enclosed impeller design are some of the features that

can be furnished by pump manufacturers to reduce axial

force in horizontal units.

Multi-stage horizontal pumps, (boiler feed water and charge

pumps for example) incorporate balance drum and a bal-

ance line. Upthrust in vertical pumps (especially those

with shorter columns) during start-up, transient and offset

conditions, is handled by thrust bearing in the driver motor.

Engineers should check the load capability of motor thrust

bearing in both directions when evaluating proposals for

vertical pumps. Typically, upthrust during start-up is 30-

35 % of the downthrust in steady state operation.

This article was originally published in ‘Pump Engineer

News’ published by KCI Publishing

www.pumpengineer.net

Pump Type

Usual Services

Typical Application Limits

Horizontal Plunger Type Pumps

High pressure, low flow in oil, water, and chemical services Flow (m³/hr):

Disch. Pressure (kPa):

2*10^5

Max. Power (KW):

150

Vertical Plunger Type Pumps

High pressure, low flow in oil, water, and chemical services Flow (m³/hr):

125

Disch. Pressure (kPa):

2*10^5

Max. Power (KW):

1 100

Horizontal Piston Type Pumps

High pressure, low flow in oil, water, and chemical services Flow (m³/hr):

450

Disch. Pressure (kPa):

7 000

Max. Power (KW):

1 500

Direct (steam driven) Acting Piston Pumps

Oils, Chemicals

The smaller the stroke length, the higher is the pump

speed. In single-acting pumps, for stroke lengths of 50

/ 100 mm, corresponding standard speeds are 750

/ 400 rpm when pumping cold water. In comparison,

in double acting design, for strokes of 50 / 100 mm,

standard speeds are 140 and 110 rpm respectively.. This

analogy applies to all types of reciprocating power pumps,

just not direct acting pumps. Speed of reciprocating

pumps depends on liquid characteristics (solids, dissolved

gases, viscosity, and temperature), NPSHA,NPSHR and

mechanical design of pump (type of valves, materials,

seals).

Flow (m³/hr):

225

Direct (steam driven) Acting Plunger Pumps

Disch. Pressure (kPa):

2 400

Max. Power (KW):

375

Flow (m³/hr):

Disch. Pressure (kPa):

14 000

Max. Power (KW):

375

Metering Pumps

(Usual Strokes: 100 – 140per minute)

Metering of chemicals in refinery, HPI industries

Flow (m³/hr):

Disch. Pressure (kPa):

5*10^4

Max. Power(KW):

Rotary Gear Pumps

NPSH is directly proportional to speed unlike pressure in

centrifugal pumps. PD pumps can create suction lift (i.e. work with

negative suction).

Lube oils, high viscosity fluids(up to 200,000cSt).

When handling viscous fluids, the net positive inlet pressure

required (NPIPR) and power increase with increasing

viscosity whereas the maximum allowable pump speed and

slip decrease.

Flow (m³/hr):

Disch. Pressure (kPa):

1 400

Max. Power(KW):

Firewater and Jockey Pumps

Fire Water Service

Follow NFPA 20guidelines

Rotary Screw Pumps

Mostly for lube oil service

Flow (m

/hr):

1 150

Disch. Pressure (kPa):

35 000

Max. Power(KW):

750

Progressive Cavity Pumps

(If required due to process fluid composition, wetted parts of

progressive cavity pumps can be furnished in titanium and

hastalloy). Consider twin screw pumps for higher than 170 deg C

operating temperature and viscosity up to 200 strokes.

Polymer dispersion, dewatering, paper and pulp, oil and

gas upstream, viscous fluids

Flow (m

/hr):

500

Diff. Pressure (kPa):

4 800

Temperature (deg C):

170

Speed (rpm):

400

Solids Content (%):

Solid Size (mesh):

<100

PUMPS AND VALVES