MTR(E), MTC, MTA - Grundfos
MTR(E), MTC, MTA - Grundfos
MTR(E), MTC, MTA - Grundfos
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<strong>MTR</strong>(E), <strong>MTC</strong>, <strong>MTA</strong> 1<br />
Minimum inlet pressure - NPSHR<br />
Calculation of the inlet pressure "H" is recommended<br />
when ....<br />
• the liquid temperature is high,<br />
• the flow is significantly higher than the rated flow,<br />
• inlet conditions are poor.<br />
To avoid cavitation, make sure that there is a minimum<br />
pressure on the suction side of the pump. The<br />
maximum suction lift "H" in feet of head can be<br />
calculated as follows:<br />
H = pb – NPSHR – Hf – Hv – Hs pb = Barometric pressure in feet absolute.<br />
(Barometric pressure can be set to 33.9<br />
feet).<br />
In closed systems, pb indicates the system<br />
pressure in feet.<br />
NPSHR = Net Positive Suction Head in feet of head.<br />
(To be read from the NPSHR curve at the<br />
highest flow rate the pump will be<br />
delivering).<br />
H f<br />
H v<br />
= Friction loss in suction pipe in feet of head.<br />
(At the highest flow rate the pump will be<br />
delivering.)<br />
= Vapor pressure in feet.<br />
(To be read from the vapor pressure scale.<br />
"H v " depends on the liquid temperature<br />
"T m ").<br />
Hs = Safety margin = minimum 2.0 feet.<br />
If the "H" calculated is positive, the pump can operate<br />
at a suction lift of maximum "H" feet of head.<br />
If the "H" calculated is negative, an inlet pressure of<br />
minimum "H" feet of head is required.<br />
H f<br />
P b<br />
Fig. 27 Minimum inlet pressure - NPSHR<br />
tm<br />
(°F)<br />
Hv<br />
(Ft)<br />
370 413<br />
360 328<br />
340 259<br />
320 203<br />
250 66<br />
230 49<br />
39<br />
212 33<br />
194<br />
26<br />
20<br />
176 16<br />
13<br />
158 10<br />
140 6.6<br />
122<br />
4.9<br />
3.3<br />
104 2.6<br />
2.0<br />
86 1.3<br />
0.9<br />
68<br />
0.7<br />
50<br />
32<br />
0.3<br />
Note: In order to avoid cavitation, never select a pump<br />
whose duty point is too far to the right on the NPSHR<br />
curve.<br />
Always check the NPSHR value of the pump at the<br />
highest possible flow rate.<br />
Q<br />
H<br />
H v<br />
300<br />
280<br />
270<br />
148<br />
131<br />
115<br />
98<br />
82<br />
TM03 4307 2006<br />
23<br />
<strong>MTR</strong>(E)