Membrane pump with sniffer measurements and interpretation

Citation for published version (APA):

Hospers, G. D. (1981). Membrane pump with sniffer measurements and interpretation. (TU Eindhoven. Vakgr. Transportfysica : rapport; Vol. R-477-D). Technische Hogeschool Eindhoven.

Document status and date: Published: 01/01/1981

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EINDHOVEN

DOCUMENTATIECENTRUM B.O.S. - THE.

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MEMBRANE PUMP WITH SNIFFER MEASUREMENTS AND INTERPRETATION

G.D. HOSPERS april 1981

Windenergy Group

Eindhoven University of Technology P.O. Box 513

5600 MB Eindhoven The Netherlands

Symbols

I. The pump 2

2. Testing equipment 3

3. Measurement procedure 4

4. Calibrations, conversions and accuracy 6

5. Results and their interpretation 8

5.1. Recommandations 9

Table of results 10

Figures: Fig. I Membrane pump with sniffer and 15 testing equipment

Fig. 2 Graphs of test results 16

Fig. 3 Graph of theoretical behaviour 17

(in combination with appendix)

References 18

SYMBOLS A M; M_nom P U V; V_s' V nom a g h; h s' hp k 1 m n p; Patm; Ps; Pp r s t u v; v* r;;

n

p <P_v w; w* Area Torque; - nominal Power Voltage

Volume; - stroke; - nominal Acceleration

Acceleration of gravity

Height; - suction; - pressure Polytropic exponent

Length Mass

Number of strokes; revolutions per minute Pressure; - atmospheric; - suction; - pressure Crankradius

Stroke Time

Displacement

Velocity; - sniffer critical Pressure loss coefficient Efficiency

Specific mass Flow of volume

1. THE PUMP

The tested pump is known as a membrane pump. An impression of it is given in figure 1. More details can be found in the drawings [ref. 1]. The test situation is an accurate copy of the field conditions in which it has worked for 1 year. This gave us the possibility to make a comparison between field and laboratory performance [ref. 2].

Some technical details of the pump:

Membrane. Material: Rubber sheet

Thickness: 4 mm

Diameter: ~ 240 mm (effective)

Stroke: 30 nun (max. 40 mm)

Valves. Lifting height: 10 nun

Diameter: $ 100 mm

Seat Diameter: $ 90 nun

Pressure airchamber volume: 9.0 1 (max. effective) Suction airchamber volume: 6.7 1 (max. effective) Pressure tube. Inside diameter: ~ 70 nun

Length: 1250 mm

Suction pipe. Inside diameter: ~ 105 nun

Lenght: 4100 nun

The sniffer is a special device to allow the·pump to run unloaded at very low speeds, which is very important for windmill applications. There is an airvalve on top. Through

this valve air can flow into the pump during the up-going stroke. The va~ve closes by the pressure drop caused by the passing air, and after that the suction begins. During the down-going stroke the air is pressed out through the same valve. It passes also a second smaller valve in the sniffer. This valve will be closed by water but not by air, thus avoiding that the water leaves the pump via the sniffer. More details about this sniffer can be found in (ref. 3] and [ref. 4]; a brief theoretical description can be found in the appendix.

2. TESTING EQUIPMENT

A general view of the testing equipment is given in figure 1. The guided pump rod is driven by a long (~ 2 m) connecting rod. The crankshaft is driven by a worm gearbox. This box can hinge along the crankshaft axis. The resulting misalignment compared to the rpm variator is taken up by a special selfadjusting teeth coupling. Another result is now that the reaction torque of the box can be measured. This is done by a strain gauge transducer, in combination with a strain meter that shows the instantaneous force.

By means of an integrator circuit (1

Mn,

19 ~F) we can read the average from the digital voltmeter. The water output is gathered in a bucket. The time for a number of strokes is found from a hand held stopwatch. To count the number of strokes we read a (continuously running) mechanical stroke counter. The amount of water during that number of strokes can be read from the balance.

Some technical data:

10) kg Motor:

Variator range:

Strain gauge transducer: Strain meter: Volt meter: Balance: Stroke counter: Stopwatch: 2.2 kW/3 Hp at 1400 RPM, coupled to variator with V-belt

I : I : 5.8

kN, 4 x 600

n

Peekel, type CA 300

Fluke, type 8010

A

(Digital) Berkel, type 3000, max. 50 (+ Mechanical type, 6 digits Mechanical type

3. MEASUREMENT PROCEDURE

Choose rpm,

Wait for stable voltage (~ 90 s)*.

Choose required number of strokes and wait for countersetting which is easy to remember.

i

Start stopwatch.

Start Shift tube from return to bucket. Measurement R_ememb_{er countersetting.}

Read and remember voltage. Notice number of strokes.

Stop

~top

stopwatch.

MeasurementlShift tube from bucket to return.

Write: Voltage (ll)

Number of strokes (n) Time (t)

Weight (m)

Empty bucket~ reset stopwatch.

Next

* The integrator circuit has an RC-time of 19 s.

~

=

RC

=

(106 n)x(19 x 10-6 F)

=

19 s. To get less than

1% error: -t

T

(1 - e ) > 0,99 + t > 4,6 T, + t > 87,55

With this procedure the measurements 1 .•. 125 have been carried out.

During measurements I ... 63 the speed has been increased only, while the behaviour of the pump is accurately studied.

During measurements 64 125 the speed has been decreased only, except for 83 .•• 92 to study the resonance effect.

In the table of results the groups of (mostly two) measurements are divided by thick lines. Within one group nothing is changed and the machine is not stopped in between the measurements.

4. CALIBRATIONS, CONVERSIONS AND ACCURACY

The only necessary calibration is that of the torque measurement system.

~~Eg-!2i~!~~~E' Turn crank to bottom on top dead center. On the strain meter we adjust voltage to zero.

!gEg~~_£!!~2E!£~g~.In the same crank position as for zero ad-justment a lever of 0.5 m length is clamped in horizontal position on the crank shaft. Read voltage U1. Now a weight of 40 N is connected to the lever at 0.5 m distance thus adding 20 Nm. Read voltage U2.

Conclusion:

The calibration in cold condition gave:

20 Nm :: (324 - 23)mV + 1 mV

It appeared that during the test the adjustment changed. The zero shifted to -2 or -3 mV. See table "calibration after measurement 63" at page 12.

The calibration check in hot condition gave:

o

Nm :: - 2.5 mV

20 NM .... (322 - 19.5) mV :: 302.5 mV

The real torque (M) in hot condition (because the adjustments were done in cold condition) can now be found with:

The stroke volume is given by:

v

s = Vtotal n

_v

_{~ m (liters)} s n p = 1000 kg/m3 1 m3 _{~ 1000 liters}

The angular speed is:

The efficiency is given by

w ~ ~ x 21T(rad/s) P out (water) p x cf>v n= = = P. Mxw ~n pgh _x

Yt.o.t.

_t pgh x

Pt

m f]= = MXE:. x 21T M x

E:.

X 2'11"

_+n

=

...

- x35 m x 100% t L 21T M x n g =·10 m/s2 h ::0 3.5 m

The accuracy of the different measurements is as follows: Torque voltage:

.!.

1.5 mV ~ + 0.1 Nm

Mass measurement:

.!.

0. I kg Time measurement: + 0.2 s

Number of strokes: no error (is.taken into account with time) Delivery height:

.!.

0,05 m

5. RESULTS AND THEIR INTERPRETATION

In the table measurements, results and remarks can be found. The measurements of the group 63 ••. 125 indicated with a dot

(0) are represented in graphs, see fig. 2. In figo 3 the results expected according the theory described in [ref. 4] are shown.

The figures show clear irregularities, see also the remarks

in the table of results. They are caused by airchamber resonances, which can be calculated with the formula [ref. 5]:

_ /k.A.p

w_o - - - -_poV.l 1.4 P

=

1000 kg/m3

=

0.00385 m2

=

105 N/m2 W o

=

6.9 rad/s

=

9 x 10-3 _m3 press

=

1.25 m 1.4 P = 1000 kg/m3

=

0,0086 m2

=

0.7xlOs N/m2 = 6.7 x 10-3 _m3 k

=

A.

pJ.pe p V 1 k

=

A. pJ.pe p V 1

=

4.1 m w o . suctJ.on

=

5.5 rad/s

We can conclude that at:

w

=

5.3

w

=

10.3

w

=

3 w

=

9.7 rad/s rad/s rad/s rad/s

Resonance suction airchamber.

Possible second-harmonical resonance suction airchamber.

Irregularity at approximately half the resonance frequency of suction airchamber. Resonance of the pressure airchamber:

difference between practical and calculated frequency (6.9 rad/s) may be caused by short pipe, which also can be half empty.

w

=

4 ••• 5 rad/s

w

> 12 rad/s

There is a very high stroke volume,

possibly we see an after admission effect. (The suction line still behaves as if undamped at this frequency.)

The torque graph is concave: Because of friction losses (L\p

=

~.!pv2) , we expected the required torque to be more and more increasing, a convex graph.

At the same time we see the stroke volume going down, while it should increase. Apparently the friction losses required a bigger expansion of the air bubble under the sniffer, thus decreasing the effective stroke volume and the required torque. A very practical conclusion from the graph could be that the efficiency graph is mu~h more influenced by the stroke volume than by the torque. Efficiency and stroke volume graph also have the same shape. This all means that> an (easy) measurement of the stroke volume can give an impression of the efficiency

(for this type of pump).

5.1. Recommendations

a) Extend theoretical description of suction pump with sniffer, in relation to

(10) stroke volume change due to friction losses in the suction line,

(20) after admission.

b) In practical applications the resonance frequencies of airchambers should be less than the minimum operating frequency (3 rad/s) of the pump.

c) Avoid to build up a pressure head, because then the membrane may buckle.

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VARIATOR

It~IIIV

,~'

"

, I

...

,

..

' ... ~

-

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...

...

,

...

"

"

kg

SAI.A.."

•

STRAIII

MlTE.l

1~\"'4w1

(

M...

A _ - - - '

FIG. I MEUBRANE PilliP WITH SNIFFER AlID TESTING EQUIPMENT

-

-

-WATER

RETURN

SNIfFER

.$r

RAIN &AU&E

.TIAliIUCEI"

--

_-

_-

_-

.

_-~

...

_{- -}

--

_{- -}

-

- -

_{- -}

-

-

_-

-

_-

~. -- -- -- --

_-

_-

_-

- - - .

_-

_-

-- -- - - - -

-- --

-

-

--

_{- - - -}

-

- - -

--

-

--

-

-- --

-

-

- -

-

--- --- --- --- --- --- ---

-REFERENCES

Drawings

"Membrane pump"

Dwg.nr. 7702-5 sheet I

&

2

2 Beurskens, Hageman, Hospers, Kragten, Lysen

"Low speed waterpumping windmills: rotor tests and overall performance"

Third International Symposium on Wind Energy Systems, August 26-29, 1980

3 Kragten

"Measurements piston pump Tunesia" (in Dutch) March 1979, R-376-D

4 Lenssen

"Matching of a single-acting piston pump and a windmill by means of a sniffer" (in Dutch)

September 1978, R-351-S

5 Hospers, Lysen

"Airchambers for piston pumps" to be published

All reports can be ordered from:

Wind Energy Group, Eindhoven University of Technology, P.O. Box 513, 5600 MB EINDHOVEN, Netherlands

APPENDIX

~!£!=E!~~_~=~~~!~~!_~!_£~£_~!E~_~~!!!=!

a) The piston (membrane) starts at bottom dead center.

u = r(I - coswt}

du .

v

=

dt

=

wr s~nwt

V

=

A.u

=

A.r(I coswt); the maximum of this is: V_nom = A.2r

b) The speed increases to v* and then the sniffer closes.

v*

=

wr sinwt ~ wt

=

arcs~n. -v*

wr

Definition: The angular speed w* is the minimum required angular speed to close the sniffer.

. w* wt

=

arCS~n

-w

In the pump now air of atmospheric pressure is present, with a volume:

w*

VI

=

A.r{1 - cos arcsin(-)}

w

c) The air is now expanded to suction pressure.

P_{a m}t

~ =

P_s

~ ~

V2

P ,lAc. w*

V2 = (.:...a.tm:r-.A.r{1 - cos arcs in(w-) } Ps

d) The suction of water begins, and stops at the top dead center. The total amount of water displaced is the real stroke volume:

v

_s

=

V_nom - V2

p ...t-..

J1<.

w

*

= A.2r - (~r.A.r{l - cos arcsin(W-)} Ps

w*

P ~k.

=

V_nom

-!V

_nom.{l - cos arcsin(--)} x

(~J--w Ps

w*

1 - cos{arcsin(-)} ~

=

1 _ { ' ...- -=-_~w_} V_nom 2

w*

Because: cos{arcsin(-)} w + 1 (see fig. 3)

e) Downward stroke: expulsion of water and air gathered during upward stroke. The air leaves the pump again through the sniffer: this costs no energy.

The average torque for a full stroke is now:

- M__ - V 1 V

M

=

.:::c.cm.~

= -.

pg (h + h ).~