Zenith B Spécifications télécharger pdf (Page 3)

Design

Zenith’s B-9000 Series precision meter-

ing pumps utilize a rotary external spur

gear which dispenses an exact volume

of fluid per shaft revolution (cc/rev).

Precision ground and lapped con-

struction, including alignment dowels,

allows for close control of operating

clearances. This ensures precise,

pulseless and repeatable flow under

varying process conditions.

Integrated closed loop speed con-

trol and a compact motor driver system

maintains up to .01% accuracy of set

point speeds and also accepts automat-

ed interfaces.

The B-9000 Series is constructed of

400 series stainless steel, providing

excellent bearing qualities (hardness 54

) and corrosion resistance for most

chemical processes. The pump offers

increased uptime while minimizing main-

tenance due to its simple design of only

three moving parts.

The B-9000 Series is a new genera-

tion of Zenith’s traditional B-Series pump.

While maintaining precise flow charac-

teristics, its optimum gear design

reduces bearing loads, while increasing

speed capability. The pump allows

direct piping and shaft engagement and

includes a single mechanical shaft seal,

(other seal types available).

Operation

Fluid enters the pump through the inlet

port located in the front plate and fills

the gear pocket. As the gears rotate, a

precise amount of fluid is trapped by the

side walls of the gear pockets and gear

teeth.

The metered fluid is transported by

the rotation of the gears to the discharge

side of the pump where the gear teeth

come into mesh. This action forces the

fluid out of the gear teeth and through

the outlet port located in the front plate.

The pressure developed is determined

by the pump size, the gear clearances,

pump speed, fluid viscosity and imped-

ance to flow.

Pump speed is limited by practical

considerations. If a high viscosity fluid is

being metered and pump speed is

increased beyond a certain point, the

fluid may not be able to fill the gear

teeth spaces, and the pump will not

obtain enough fluid to maintain normal

volumetric efficiency. Lack of sufficient

fluid is called starvation or cavitation.

This can be remedied by increasing the

inlet pressure or reducing pump speed.

See table 1 on page 5.

Metering of thin fluids requires a

different approach. Since the pump

depends upon the metered fluid for

lubrication of internal bearing surfaces,

speeds are normally limited. These

bearing surfaces include the bearing

areas in the front and rear plates, and

the driver gear turning about the arbor.

Accelerated wear and even seizure may

be the result of high speeds, especially

if attended by low lubricity or a fluid

containing abrasive particles. In certain

applications, it is recommended to use a

pump of larger capacity operated at a

lower speed. Contact our Applications

Engineering Department for assistance.

Pump efficiency depends on four

basic variables: fluid viscosity, gear

clearances, differential pressure and

pump speed. The less viscous the fluid,

the more likely it is to flow through a

given orifice. In a Zenith pump, this

orifice is the gear clearance. Differential

pressure forces the fluid through this

clearance at a steady rate, regardless

of the pump speed. Thus, the slip is

constant for a given amount of time. The

actual delivery of fluid is the measured

delivery minus the slip. If we increase

the pump speed we increase the mea-

sured delivery, while the slip remains

constant, causing the pump to become

more efficient. Likewise, if we slow the

pump down, the pump becomes less

efficient. Slip is repeatable and pre-

dictable, and pump operation can be

adjusted to compensate and, thus,

accuracy is very high. See Graph 1 on

page 5.

Zenith B-9000 Series pumps are

designed for operating temperatures

less than 645°F. When operating at

temperatures above ambient, heat

jackets should be used, and pumps

should be heated slowly and uniformly

to avoid warpage and internal component

interference.

The 400-Series stainless steels used

in the construction of the B-9000 Series

pumps provide sufficient corrosion

resistance for most standard chemical

processes. The material hardness will

provide a high degree of wear resistance

as well. However, processes involving

corrosive or abrasive fluids should

always be reviewed by Zenith.

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