Method of and stand for determining cavitation characteristics of pumps

FIELD: mechanical engineering; testing facilities.

SUBSTANCE: invention can be used for stand tests of pumps of any application. According to proposed method full pressure at pump input is maintained constant by means of reservoir with free surface of liquid exposed to constant (atmospheric) pressure installed in intake pipeline. Working liquid saturated vapor pressure at pump input is changed by heating. Periodical measurement of required parameters in process of liquid heating makes it possible to calculate sought for cavitation margin Δh. Method is implemented by test stand containing pump to be tested, output throttle, flow meter, heat exchanger, service tank, pipe fittings, all arranged in closed hydraulic circuit, and reservoir with free surface of working liquid in combination with capsule made of heat conducting material connected to circuit at pump input. Space of capsule is divided into two parts, one of which is partly filled with working liquid and sealed, and other communicates with circuit.

EFFECT: improved accuracy of measurements and simplified determination of pump cavitation characteristics.

3 cl, 1 dwg

 

The proposed method is applicable in pump building, all organizations involved in the investigation and development of pumps for any purpose.

Cavitation characteristic of the pump is called the dependence of fluid flow and pump head h of NPSHA Δh.

The known method of removing cavitation characteristics of pumps operating in a closed hydraulic circuit, the stand containing the pump, the input choke installed before the pump, output choke, connecting piping, measuring devices. The essence of the method is that the input through the inductor, the change of the total pressure P1* before the pump at a fixed position of the output inductor. This measures the total pressure P1* at the entrance to the pump and other parameters in accordance with the requirements of GOST 6134-58 “centrifugal Pumps, axial and swirl”.

The disadvantage of this method is that, under certain provisions cover the input choke in the narrowing of the cross section itself provokes cavitation, which occurs earlier than the cavitation in the pump, affecting the latter. In the cavitation breakdown in the pump comes on high inlet pressures, i.e. anti-cavitation resistance deteriorates.

The disadvantage of the actual stand is ugodnog the throttle, which regulate the pressure at the entrance to the pump and which, by changing the cross-section of the inlet pipeline, creates conditions for the development of cavitation in this section, penetrating into the liquid end of the pump and alter their work (see Karelin VIA Cavitation in centrifugal and axial pumps, s, Fig, s. Moscow, Motor Cycle", 1963).

The closest technical solution to the present invention is a method of removing the cavitation characteristics of pumps and a matching stand, holding the test pump, supply tank, a flow meter, tank, and pipe fittings (SU 1399503 AND, KUZIN, Y.M. and others, 30.05.1988).

The principal disadvantage of this method is the impossibility of removing the cavitation characteristics at low pressures and, moreover, when the negative pressure at the entrance to the test pump 4, because, judging by the diagram in the drawing, before the test pump will always be a pressure that will not allow disruptive branch characteristics, without which the cavitation performance is meaningless. To get a stall branch before the test pump 4 to create a negative pressure in the tank 1, but in this case, the cavitation breakdown will occur in the pre-supply pump and will provoke the development of cavitation in the pump 4 on a regular cavitation free operation. It turns out that the known method, in the best case, suitable only for pumps cavitating p and sufficiently large input pressures.

The disadvantage of the stand, resulting from the disadvantage of this method is the impossibility of removing the cavitation characteristics of the pump 4 in full due to the presence of the pump 2, which makes the stand was not fit for purpose, in other words, unusable. It should be noted that the stand is fairly complex - contains attributes, without which you can do: vacuum system, pressurization system tank 1, a feed pump 2, additional shut-off equipment.

The task is to increase the accuracy and to simplify the removal of the cavitation characteristics of pumps.

The technical result aimed at solving the problem, provided that form a closed hydraulic circuit, pumped through him pump the working fluid, measured at a given full inlet pressure to the pump and the output from it, measure the temperature at the inlet to the pump, and fluid flow, while the total pressure at the inlet to maintain a constant pump, change the saturated vapor pressure at the inlet to the pump, determine the pump head and cavitation margin formulas

where H is the pump head;

P2* - the total pressure at the outlet of the pump;

P1* full pressure at the inlet to the pump;

ρ - density, temperature-dependent;

Δh - kavit the operating margin;

Psis the saturated vapor pressure, the temperature-dependent.

Task related to the stand, is the implementation of the proposed method of removal cavitation characteristics.

The technical result is achieved by the fact that in the stand to determine the cavitation characteristics of the pump containing installed in a closed hydraulic circuit test pump, flow meter, heat exchanger and tank and pipe fittings, according to the invention to a closed path in front of the pump attached to the tank with a free surface of the fluid and capsule of heat conducting material with a flexible membrane separating the cavity of the capsule into two cavities, one of which is sealed and filled with the working fluid and the other hydraulically communicates with a closed circuit between the pump and the flow meter has an output choke.

The drawing shows the stand. The stand includes a pump 1, engine 2, resulting in a rotation of the pump 1, the tank 3 from the nozzle 4 having a valve 5, the output inductor 6, a flow meter 7, mesocephalic 8, tank 9, the valves 10 and 11, the pressure gauges 12 and 13, thermocouple 14, the capsule 15 with membrane 16 that separates the cavity 17 and 18 of the capsule 15, digital recorder 19, fixing the deformation of the membrane 16, the connecting pipelines.

The essence of the method is aasnaes work stand. In the input line installed capacity of 3 from the free liquid surface, communicating with the atmosphere through pipe 4 at an open gate valve 5. Start the engine 2, set at a given frequency of rotation of the pump the throttle 6 in the position corresponding to the specified flow rate, heat the liquid and periodically as heat (altenaria) fluid at several values of temperature measured total pressure P1* and P2* at the entrance to the pump and when exiting, respectively, the pressure gauges 12 and 13, the temperature T1at the entrance to the pump - probe 14, the flow rate Q is the flow meter 7. Then calculate the pump head

cavitation margin

where Psis the saturated vapor pressure (determined by the tables as function of temperature);

ρ - density of fluid (as determined by the tables as function of temperature),

and build cavitation characteristics.

As specified mode atmospheric pressure PHand the height of the liquid column in the vessel 3 above the axis of the pump 1 remains practically with very small deviations unchanged, and the total pressure P1* also does not change. Therefore, cavitation margin Δh is actually only a function of temperature T1i.e.

Thus, by measuring the heating process (altenaria) fluid temperature T1get cavitation margin, without resorting to additional systems vacuum or boost.

If for any reason the circuit cannot have a temperature above acceptable level, then the circuit is connected through valve 2 mesocephalic 8, fed by cold water from a supply tank 9, the consumption of cooling water (inlet through the valve 10 and the drain through the valve 12) is adjusted to allowable temperature in the circuit remained unchanged. Then all the above operations are performed when autokarowe fluid in the circuit is not higher than the permissible and the navigation feature of the pump is constructed in the range of temperatures T1from its initial value to valid.

The described method is applicable when the subjects pumps have a high enough anticavitation quality, cavitation failure comes to them when the inlet pressure P1* login, less atmospheric. In that case, it is known that this pressure will be below atmospheric, which is very rarely, the space above the free surface in the tank 3 naduvath technical air through the pipe 4 and seal the container 3 by closing the valve 5. Previously between the pump 1 emkosti 3 install the capsule 15, having two cavities 17 and 18, separated by a highly sensitive membrane 16, and the cavity 17 is partially filled with the working fluid and the cavity 18 report from the circuit, leaving the outer wrap both cavities thread. Thus, during operation of the pump in the cavity 17 is the vapor pressure PSthe working fluid in the cavity 18 - total pressure P1*. Under the action of differential ΔP these pressures, the membrane will Flex and will generate a signal on the digital recorder 19, whereby in addition to the above measurements measure the difference of P1* - PS. According to measurements, as before, compute the values N, Δh and build cavitation characteristics.

1. The method for determining the cavitation characteristics of the pump, namely, that form a closed hydraulic circuit, pumped through him pump the working fluid, measured at a given full inlet pressure to the pump and the output from it, measure the temperature at the inlet to the pump, and fluid flow, characterized in that the total pressure at the inlet to the pump to maintain a constant, changing the pressure of saturated steam at the inlet to the pump, determine the pump head and cavitation margin formulas

where H is the pump head;

P2* - the total pressure at the outlet of the pump;

p num="43"> P1* full pressure at the inlet to the pump;

ρ - density, temperature-dependent;

Δh - cavitation margin;

PSis the saturated vapor pressure, the temperature-dependent.

2. Stand to determine the cavitation characteristics of the pump containing installed in a closed hydraulic circuit test pump, flow meter, heat exchanger and tank and pipeline valves, wherein the closed loop before the pump attached to the tank with a free surface of the fluid and capsule of heat conducting material with a flexible membrane separating the cavity of the capsule into two cavities, one of which is sealed and filled with the working fluid and the other hydraulically communicates with a closed circuit between the pump and the flow meter has an output choke.



 

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FIELD: mechanical engineering; testing facilities.

SUBSTANCE: invention can be used for stand tests of pumps of any application. According to proposed method full pressure at pump input is maintained constant by means of reservoir with free surface of liquid exposed to constant (atmospheric) pressure installed in intake pipeline. Working liquid saturated vapor pressure at pump input is changed by heating. Periodical measurement of required parameters in process of liquid heating makes it possible to calculate sought for cavitation margin Δh. Method is implemented by test stand containing pump to be tested, output throttle, flow meter, heat exchanger, service tank, pipe fittings, all arranged in closed hydraulic circuit, and reservoir with free surface of working liquid in combination with capsule made of heat conducting material connected to circuit at pump input. Space of capsule is divided into two parts, one of which is partly filled with working liquid and sealed, and other communicates with circuit.

EFFECT: improved accuracy of measurements and simplified determination of pump cavitation characteristics.

3 cl, 1 dwg

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