Nova-Tech LMI Series G - SD Metering Pump - Manual (Page 8)

1.2 PRINCIPLES OF OPERATION
Drive Assembly (See Figure 2)
The pump consists of two major assemblies; the drive
and the liquid end. Pump delivery is a function of the
drive's stroke rate, liquid end size and stroke length.
Stroke length can be increased while the pump is run-
ning by counterclockwise turning of the stroke adjust-
ment knob. The drive assembly works on the principle
of a variable eccentric. The rotational motion of the motor
is transmitted by the worm (1) to the worm gear (2)
which is linked to an eccentric system (3). The eccen-
tric system then converts the rotary gear motion into
linear reciprocating motion of the connecting rod (4). At
0% capacity setting, the connecting rod axis (B) is
aligned with the gear axis (A) and no movement of the
connecting rod takes place. At 100% capacity setting,
an eccentricity exists between the connecting rod axis
(B) and the gear axis (A) which results in linear move-
ment of the connecting rod and resulting pumpage.
Drive parts (See Fig. 8 for limited drive parts available)
are no longer sold by Milton Roy. When drive parts are
found to be bad a complete new painted pump body
with all gears, stroke controls, etc. can be purchased
from Milton Roy. The customer will only need to mount
the liquid end/motor from the existing pump.
Mechanically Actuated Diaphragm Liquid End
(See Figure 2)
The diaphragm assembly (5) is mechanically linked to
the connecting rod (4) and has the same reciprocating
motion. As the diaphragm starts back on the suction
stroke, the pressure immediately drops inside the liq-
uid end. When the pressure in the liquid end drops
below the suction line pressure, the suction ball check
is “pushed” upward and the process fluid in the suction
line flows into the liquid end chamber (diaphragm head).
When the suction stroke ends, the diaphragm move-
ment momentarily stops and the pressure in the liquid
end equalizes with the pressure in the suction line caus-
ing the suction ball check to reseat.
NOTE: It is important that the pressure in the
liquid end remain above the vapor pressure of
the process fluid during the suction stroke. If
the fluid pressure drops below the vapor pres-
sure, cavitation will occur which will have a nega-
tive impact on the performance of the pump.
If you suspect the possibility of cavitation, con-
tact your dealer for assistance.
Figure 2:
Stroke Control Operating
Principle
(A)
(B)
(A) (B)
(A)
(B)
Zero Stroke Setting
Discharge Phase Suction Phase
Setting to Maxmum Stroke
1
2
3
4 Worm
Worm Gear
Eccentric
Connecting Rod 5
6
7
8 Diaphragm
Stroke: two times the distance between (A) and (B)
Position at rear neutral point
Position at forward neutral point
1
2
4
5
3
7
6
8
2