УДК 697.32

BYPASS REGULATION FOR CENTRIFUGAL PUMPS

Nicolay D. Andriychuk, Manolis V. Pilavov

The abstract - rational area of efficiency bypass regulations of centrifugal pumps is specified. The criteria that limited this area is obtained.

Keywords: efficiency, a ventilator characteristic, bypass regulation.

Summary - Bypass regulation using rational area is determined. Area bounding criteria is obtained.

Key words: flow rate, ventilator characteristics, bypass regulation, efficiency.

Water supply systems carry out the major function of water supply and distribution to consumers. Quality of distribution and water supply appreciably depends on methods of regulation of the water discharger in system [1]. This process is carried out in several ways: throttle control by means of the regulating control devices established on an input or an exit of system of water supply, frequency rotation changing of the driving wheel of the pump, etc.

Each of these ways has the advantages and lacks. There is one more way of regulation of productivity of pump installation – use bypass. This way is used at regulation of productivity of centrifugal pumps, however in the literature and engineering practice there are no data on sphere of its application though simplicity of its realization, depth of regulation, reliability can appear in some cases decisive at creation of systems of automatics.

The reason of it, as our researches have shown, are uncertainty of profitability bypass way of regulation of the productivity, depending on characteristics of the pump, a network, position of operating point etc. In offered work the problem of definition of profitability bypass way of productivity pump regulation, rational area of its application was presented.

The elementary scheme bypass control is presented on fig. 1. The water discharge in system, Q_c changes due to full or partial opening of the parallel channel to system (bypass line). The delivery Q_о in bypass line is adjusted by control device (РО). The pump delivery Q is defined by expression

Q = Q_c + Q_о (1)

Fig. 1. Design diagram

Н – the pump; РО – control device in bypass line

For estimation of bypass regulations efficiency in co-ordinates system of delivery-pressure is considered by following characteristics (fig. 2):

Pump characteristic P_v (Q);

The characteristic bypass line P_б (Q);

The characteristic of network P_c (Q) as which it is understood the equivalent characteristic of system and bypass line.

Fig. 2. To an efficiency estimation for bypass regulations

The characteristic of a network before opening bypass line on fig. 2 is designated as P'_c (Q). After opening of bypass line the new characteristic of network P "_c (Q) turns out addition under the delivery of characteristics of bypass line P_б (Q) and the old characteristic of network P'_c (Q). The delivery arriving in a network (it is pump delivery) is designated through Q" which includes the delivery in bypass line Q_о and new delivery Q "_c that less then delivery in system Q'_c before opening bypass line.

Supposing that efficiency of the pump is constants in a regulation zone, it is possible to confirm the following.

Bypass regulation has efficiency if the capacity given to a network by the pump, decreases at opening bypass line, i.e.

(2)

or

(3)

Let's underline, that here Q ', Q "– delivery of the pump before inclusion bypass line.

Considering, that pressure P_v developed by the pump, is pressure for network P_с

(4)

On the basis of (2) and (4) condition of efficiency formulated above is

(5)

or

(6)

Whence we receive

(7)

The criterion (7) allows to formulate an efficiency condition bypass control as follows.

Efficiency bypass control of pump installation for system of water supply takes place, if for an initial pump’s operating point pump’s characteristic satisfies to criterion

(8)

or

. (9)

The carried out analytical researches have allowed to find rational area of use bypass control of pump’s productivity, in which its efficiency above, than at the traditional throttle. The criterion defining expediency of use bypass control is received.

The executed experimental researches were completely confirmed the obtained data.

Literature

1. Коваленко А.А. Гидравлические и аэродинамические машины. – Луганск: Издательство Донбасской ГАСА, 2000. – 77с.