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Lowara CO 350/03/A 107350090 [14/19] Npsh npsh npsh npsh npsh
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15
The minimum operating values that can be reached at the
pump suction end are limited by the onset of cavitation.
Cavitation is the formation of vapour-filled cavities within
liquids where the pressure is locally reduced to a critical value,
or where the local pressure is equal to, or just below the
vapour pressure of the liquid.
The vapour-filled cavities flow with the current and
when they reach a higher pressure area the vapour
contained in the cavities condenses. The cavities collide,
generating pressure waves that are transmitted to the
walls. These, being subjected to stress cycles, gradually
become deformed and yield due to fatigue. This
phenomenon, characterized by a metallic noise
produced by the hammering on the pipe walls, is called
incipient cavitation.
The damage caused by cavitation may be magnified by
electrochemical corrosion and a local rise in
temperature due to the plastic deformation of the
walls. The materials that offer the highest resistance to
heat and corrosion are alloy steels, especially austenitic
steel. The conditions that trigger cavitation may be
assessed by calculating the total net suction head,
referred to in technical literature with the acronym
NPSH (Net Positive Suction Head).
The NPSH represents the total energy (expressed in m.)
of the liquid measured at suction under conditions of
incipient cavitation, excluding the vapour pressure
(expressed in m.) that the liquid has at the pump inlet.
To find the static height hz at which to install the
machine under safe conditions, the following formula
must be verified:
hp + hz ≥ (NPSHr + 0.5) + hf + hpv
where:
hp is the absolute pressure applied to the free liquid
surface in the suction tank, expressed in m. of
liquid; hp is the quotient between the barometric
pressure and the specific weight of the liquid.
hz is the suction lift between the pump axis and the
free liquid surface in the suction tank, expressed
in m.; hz is negative when the liquid level is
lower than the pump axis.
hf is the flow resistance in the suction line and its
accessories, such as: fittings, foot valve, gate
valve, elbows, etc.
hpv is the vapour pressure of the liquid at the
operating temperature, expressed in m. of
liquid. hpv is the quotient between the Pv vapour
pressure and the liquid’s specific weight.
0,5 is the safety factor.
The maximum possible suction head for installation
depends on the value of the atmospheric pressure
(i.e. the elevation above sea level at which the pump
is installed) and the temperature of the liquid.
To help the user, with reference to water temperature
(4° C) and to the elevation above sea level, the
following tables show the drop in hydraulic pressure
head in relation to the elevation above sea level, and
the suction loss in relation to temperature.
Friction loss is shown in the tables at pages 16-17 of
this catalogue. To reduce it to a minimum, especially
in cases of high suction head (over 4-5 m.) or within
the operating limits with high flow rates, we
recommend using a suction line having a larger
diameter than that of the pump’s suction port.
It is always a good idea to position the pump as close
as possible to the liquid to be pumped.
Water
temperature (°C) 20 40 60 80 90 110 120
Suction
loss (m) 0,2 0,7 2,0 5,0 7,4 15,4 21,5
Elevation above
sea level (m) 500 1000 1500 2000 2500 3000
Suction
loss (m) 0,55 1,1 1,65 2,2 2,75 3,3
NPSHNPSH
NPSHNPSH
NPSH
TECHNICAL APPENDIXTECHNICAL APPENDIX
TECHNICAL APPENDIXTECHNICAL APPENDIX
TECHNICAL APPENDIX
Содержание
- Co series 1
- Enntech 1
- Applica applica applica applica applications tions tions tions tions 2
- Co co co co co com com com com com 60 hz series 60 hz series 60 hz series 60 hz series 60 hz series 2
- Market sectors market sectors market sectors market sectors market sectors civil industrial 2
- Open impeller open impeller open impeller open impeller open impeller centrifugal centrifugal centrifugal centrifugal centrifugal electric electric electric electric electric pumps and pumps and pumps and pumps and pumps and threaded threaded threaded threaded threaded connections connections connections connections connections 2
- Co com series co com series co com series co com series co com series list of models and t list of models and t list of models and t list of models and t list of models and table of ma able of ma able of ma able of ma able of materials terials terials terials terials 4
- Denominazione modelli serie co 4
- Materiali co 4
- Co com series co com series co com series co com series co com series mechanical seal mechanical seal mechanical seal mechanical seal mechanical seal 5
- Complete pump pres complete pump pres complete pump pres complete pump pres complete pump pressure tempera sure tempera sure tempera sure tempera sure temperature opera ture opera ture opera ture opera ture operating ting ting ting ting limits with any of the seals listed abo limits with any of the seals listed abo limits with any of the seals listed abo limits with any of the seals listed abo limits with any of the seals listed above ve ve ve ve 5
- List of ma list of ma list of ma list of ma list of materials terials terials terials terials 5
- Seal types seal types seal types seal types seal types 5
- Co 350 series co 350 series co 350 series co 350 series co 350 series opera opera opera opera operating characteristic ting characteristic ting characteristic ting characteristic ting characteristics a s a s a s a s at 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles 6
- Dati elettrici serie co350 2 poli 60 hz 6
- Electrical da electrical da electrical da electrical da electrical dattttta a a a a a a a a at 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles 6
- Hydra hydra hydra hydra hydraulic performance t ulic performance t ulic performance t ulic performance t ulic performance table a able a able a able a able at 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles 6
- Tabella di prestazioni idrauliche serie co350 2 poli 60 hz 6
- Motori monofase per serie co 60 hz 2 poli 8
- Motori trifase per serie co ie2 60 hz 2 poli 8
- Motors for co series motors for co series motors for co series motors for co series motors for co series 8
- Single phase motors a single phase motors a single phase motors a single phase motors a single phase motors at 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles 8
- Three phase motors a three phase motors a three phase motors a three phase motors a three phase motors at 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles 8
- A aa aav vv vvailable v ailable v ailable v ailable v ailable vol ol ol ol oltttttages ages ages ages ages motors for co series motors for co series motors for co series motors for co series motors for co series 9
- Co series co series co series co series co series dimensions and weights a dimensions and weights a dimensions and weights a dimensions and weights a dimensions and weights at 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles t 60 hz 2 poles 10
- Co series dimensions and weights 2 poli 60 hz 10
- Enntech 11
- Typical applica typical applica typical applica typical applica typical applications of co series electric pumps tions of co series electric pumps tions of co series electric pumps tions of co series electric pumps tions of co series electric pumps 13
- Npsh npsh npsh npsh npsh 14
- Technical appendix technical appendix technical appendix technical appendix technical appendix 14
- Flow rate nominal diameter in mm and inches 15
- H l min 15 20 25 32 40 50 65 80 100 125 150 175 200 250 300 350 400 1 2 3 4 1 1 1 4 1 1 2 2 2 1 2 3 4 5 6 7 8 10 12 14 16 15
- Hr flow resistance for 100 m of straight pipeline m v water speed m s 15
- Technical appendix technical appendix technical appendix technical appendix technical appendix 15
- Tttttable of fl able of fl able of fl able of fl able of flow resist ow resist ow resist ow resist ow resistance in 100 m of straight cast ance in 100 m of straight cast ance in 100 m of straight cast ance in 100 m of straight cast ance in 100 m of straight cast iron pipeline hazen iron pipeline hazen iron pipeline hazen iron pipeline hazen iron pipeline hazen williams formula c 100 williams formula c 100 williams formula c 100 williams formula c 100 williams formula c 100 15
- Fl fl fl fl flow resist ow resist ow resist ow resist ow resistance ance ance ance ance tttttable of fl able of fl able of fl able of fl able of flow resist ow resist ow resist ow resist ow resistance in bends v ance in bends v ance in bends v ance in bends v ance in bends val al al al alves and ves and ves and ves and ves and ga ga ga ga gates tes tes tes tes 16
- Tabella lunghezza di tubazione equivalente 16
- Technical appendix technical appendix technical appendix technical appendix technical appendix 16
- The flow resistance is calculated using the equivalent pipeline length method according to the table below 16
- The table is valid for the hazen williams coefficient c 100 cast iron pipework for steel pipework multiply the values by 1 41 for stainless steel copper and coated cast iron pipework multiply the values by 1 85 when the equivalent pipeline length equivalent pipeline length equivalent pipeline length equivalent pipeline length equivalent pipeline length has been determined the flow resistance is obtained from the table of flow resistance the values given are guideline values which are bound to vary slightly according to the model especially for gate valves and non return valves for which it is a good idea to check the values supplied by manufacturers 16
- Further product selection and document further product selection and document further product selection and document further product selection and document further product selection and documenta aa aation tion tion tion tion 17
- Technical appendix technical appendix technical appendix technical appendix technical appendix 17
- Xylect xylect xylect xylect xylect 17
- Enntech 19
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