## MCSF calculation?

## MCSF calculation?

(OP)

Anyone know of a method of calculating the Minimum Continuous Stable Flow of an end suction centrifugal pump? A rule-of-thumb or similar would be of help. Not able to find out as the manufacturer Rhodes-Brydon-Yuatt is long since defunct, and the pump manufactured in the 1960's

## RE: MCSF calculation?

## RE: MCSF calculation?

## RE: MCSF calculation?

1. Minimum continuous stable flow for pumps with discharge 1.5" and larger: 30% of the BEP for the rated diameter. Smaller discharges need only 10% of the BEP for the rated diameter.

2. Minimum continuous thermal flow:

Q = 5.09(HP)/[(Δt)(SGxc)]

Where:

Q = gpm

HP = horsepower at or near shutoff.

Δt = allowable temperature rise based on service,

^{o}F.SG = specific gravity of fluid.

c = specific heat of fluid (i.e., Water=1.0, HC=0.3-0.6).

## RE: MCSF calculation?

thanks

John

## RE: MCSF calculation?

The estimating formula (Sulzer) for the thermal minimum flow in metric units:

_{min}= (P.3600)/(ρ.c.Δt)where

Q

_{min}= m^{3}/hP = power, kW

ρ = density of the fluid, kg/m

^{3}c = specific heat of the fluid, (kJ/kgK)

Δt = permissible heat up,

^{o}C## RE: MCSF calculation?

## RE: MCSF calculation?

## RE: MCSF calculation?

Budris,A.R.,1989, "Sorting Out Flow Recirculation Problems", Machine Design, 8/16/89, pp.113-116

Suction Recirc.Factor,SRF=SSSxU_1txSG

LwrLim UprLim MaxSSS MaxU_1txSG

Radial Suction Impeller 550,000 710,000 14,000 80

End-suction Impeller 830,000 950,000 16,000 100

End-suction Inducer 1,400,000 Same --- 120

O'Keefe,W.,1988,"Can State-of-the-Art Research and New Experience Save Your Pumps?", Machine Design, Dec.,pp.39-44

Gam=Hub diameter/Eye diameter MFF=Minimum Flow Fraction

SSS=Suction Specific Speed(US units)

Gam=0 Gam=0.5

SSS MFF MFF

8500 0.35 0.45

16000 0.70 0.80

17500 --- 1.0

19000 1.0 ---

Lobanoff,V.S.&Ross,R.R.,1985,"Centrifugal Pumps-Design and Application, Gulf Publishing Co.

Fig.9-7 Stable Operating Window vs Suction Specific Speed

for 4-Inch(??) pump tested with 8 impellers having same blade profile but different impeller eye geometries. Results may differ for other designs but trend should be similar (following are eyeball estimates for 0.2 FF grid).

SSS Min.FF MaxFF

7000 0.50 1.25

8000 0.57 1.22

9000 0.60 1.19

10000 0.64 1.16

11000 0.68 1.14

13000 0.78 1.11

20000 0.95 1.06

## RE: MCSF calculation?

Suction recirculation onset was found at 0.62QD with pressure pulsations increasing from 10psi p-p at .62-.90QD to 60psi p-p maximum at 0.40QD. Discharge recirculation onset occurred at 0.51QD rising from 20psi at .51-.80QD to 88psi maximum at 0.3QD. Scaling the preesure-time plots at 1000GPM(0.592QD) and 300GPM(0.178QD) I found p-p pressure spikes of 40-45.5psi,and 80-112psi,respectively. The frequencies of spikes were scaled to be 235-244 Hz which is close to 4X suggesting that they are impeller blade passing peaks from a 4-blade impeller. At 300 GPM, there was also a pressure surge cycle scaled to be 5.37Hz (0.0895X). Unreported parameters derived approximately, assuming water tests at SG=1, 3600RPM and pump designator to represent pipe discharge, pipe inlet and impeller discharge diameters are HD=211ft(91.34psi), SS=1888(US), NPSHD=18.1ft.,inlet pipe velocity=11.03fps, discharge pipe velocity=19.6fps, impeller inlet tip speed=125.66fps, impeller discharge peripheral speed=172.79fps.

The SSSxU1t at SG=1 is 1,482,788 and the 125fps U1t value suggest that an inducer is needed if the pump has end suction based on Budris' criteria cited before. The 0.62QD minimum flow for suction recirculation is somewhat better than the previously cited Lobanoff & Ross Qmin stability limit of roughly 0.73QD for SSS=11,800.

## RE: MCSF calculation?

Pump Type 0.5 FF 1.0 FF

MS 5536 11542

DS 6580 13420

SS 7623 15229

IN 10823 20841

RLF 1.0 0.5

The 7 other factors or erosion parameters considered besides SSS in impeller erosion pump lifetime estimates are available NPSH, fluid thermodynamics, fluid corrosion, impeller material, speed, flow fraction,and operating hours per year(8000=1.0). An example for a large boiler feed pump results in a lifetime factor of 0.504 (with a factor of 1.0 being approximately 10 years)based on the product of the eight factors.