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Description of a pulsation damper and how it works - Hidracar

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Description of a pulsation damper and how it works A pulsation damper is a vessel with gas inside, normally NITROGEN. The initial filling or inflating gas pressure inside the dampener is always lower than the circuit pressure. The inflating gas pressure will be called “Po”. In all pulsation dampers there is an element to isolate the gas from the circuit liquid; its main function is to avoid the gas loss. This piece that separates both fluids is made basically with two materials: With rubber – Nitrile, EPDM, FPM, Butyl, Silicone, etc and thermoplastic usually PTFE. When the rubber is used the dampener is defined as bladder or bag type and if the PTFE is used the dampener can be membrane or bellows type according to the separator element form. The use of one type or another to separate material and form-bladder, membrane or bellows- will depends generally on the special performances of the circuit such as: the pressure, temperature and the possible corrosive effect that could be produced by the circuit liquid.

The performance of a pulsation damper in a hydraulic circuit with a dosing or metering pump-with piston or membrane- is to stabilise the variable and oscillating flow in each revolution of such type of pumps.( we will see later the characteristics of this types of pumps) The main performance of this pumps is to deliver a constant volume of liquid during one complete revolution with independence of the circuit resistance or pressure. When a pulsation damper has been installed the volume supplied by the pump during a complete rotation or work cycle is divided in two parts; one is going to the circuit needs and the other part goes into the pulsation dampener. This volume stored into the dampener is returned immediately to the circuit while the pump is in its suction cycle. To the amount of liquid going into and out of the dampener in each cycle or pump revolution we will call “dv”. When “dv” is introduced into the dampener the gas filled inside will reduce its volume and increase its pressure, the final gas volume plus the volume of liquid introduced will be equal to the initial gas volume. The initial gas volume is the total dampener volume or the dampener size. The dampener size is the unknown value to calculate and that will depend in all cases on the pump performances. To the dampener size we will call “Vo” We can establish that : V2 + dv = Vo, ( V2 is the final gas volume) Each dampener has a constant which depends on the charging gas value and its size ; Po x Vo = constant. When the dampeners are working is not convenient that all the liquid stored goes out in each cycle keeping the dampener empty of liquid, this will damage prematurely the bladder or the membrane when the insert fixed on it is hammered against the dampener internal bottom. We will have a new formula : V2 + dv + v = Vo Where “v” is a non used volume of liquid inside the dampener; as a norm this volume is the 10% of the total dampener volume the former formula will change to: V2 + dv + 0,1Vo = Vo; and from this Vo = ( V2 + dv ) / 0,9 The following graph and the figure representing the three states of gas volume inside the dampeners will made more clear everything exposed above.

http://www.pulsation-dampers-hidracar.com/products/pulsation%2Bdampers/technica... 2014-02-19

Description of a pulsation damper and how it works - Hidracar

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This graphs shows ; At charging gas value “Po” there is no liquid inside the dampener. The curve cuts the ordinate axis in the point where corresponds a zero value in the abscissa axis. The pressure “P1” is the gas pressure when the volume “v” has been introduced into the dampener; the pressure “P2” is the value reached by the gas when the additional volume “dv” is into the dampener . From this curve we can see that for a fixed dampener size if the value “dv” increases then the pressure value “P2” will also increase, or if we increase the dampener size keeping constant the value “dv” the final pressure gas value “P2” will be lower.

Next >> Políg. Ind. "Les Vives", s/n. - Apdo. 35 - 08295 SANT VICENÇ DE CASTELLET (Barcelona) España Tel.: +34 938330252 - Fax: +34 938331950 - [email protected] - aviso legal - © 2006 Hidracar.com


Pulsation dampers size calculation - Hidracar

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Pulsation dampers size calculation

The data needed to calculate the dampener size are : “dv” = volume of liquid that the dampener must store ( in the different types of pumps described below we will see the relation between “dv” and the capacity per revolution of each type of more used pumps ) “P1” y “P2” are the mini. and maxi. pressure values that are accepted in the circuit. Lets see an example: If the theoretical or work pressure is “Pt” and the residual pulsation admitted is +,- 5% of this pressure, the P1 y P2 values will be ; P1 = Pt - ( 5/100 ) x Pt, and P2 = Pt + ( 5/100 ) x Pt Note: The “Pt” pressure is that created at the outlet port of the pump Knowing all this data dv ,P1 and P2 we can already calculate the dampener size “Vo” From the gases compressed law (we will made some comments about this equality for this application) in isothermal conditions called Boyle law we have the expression; Po x Vo = P1 x V1= P2 x V2= Constant. (1)

If We have And also From

V1 = Vo – v, V1 = 0.9xVo V2 =V1- dv Po=0.9xP1

(1) and (2) we obtain

and (2) (3) (4)

v = 0.1xVo

Finally from; (1) (2)(3)and(4) we will obtain PoxVo=P2xV2 ; 0.9P1xVo=P2x(V1-dv) =P2(0.9Vo-dv) from the underlined equalities we have the final formula P2 x dv Vo= -----------------0.9 ( P2-P1) This is the theoretical simplified formula to calculate the dampener volume in function of ; dv, P1 and P2. As we have already said, that the charging gas “Po” = 0.9P1, this relation between Po and P1 has been taken to avoid the complete liquid empty from the dampener in each work cycle. Having this extra quantity of liquid “v” into the dampener it will compensate the possible variations of gas pressures due to external temperatures variations, and consequently the theoretical “dv” calculated could not be introduced or stored into the dampener. The former formula (1) PoxVo=P1xV1= ------ does not comply in the practice ,because when a volume of gas is compressed (in a short time) the temperature rises making an extra increase of the pressure and when the gas expands its pressure drops an extra value because the temperature is reduced-effect refrigeratorThis effect is produced in all the majority of gases, Nitrogen and air included which are the more common used for charging the dampeners ( the atmospheric air can be used for pressures less than 10 Bar ,and always when there is not any chemical reaction between the oxygen in the air and the liquid pumped ) The formula (1) will be transformed; g g PoxVo=P1xV1= --------g= specific heat relation of the gas at constant pressure and volume . For the majority of gases, g = 1.41 .This constant is also theoretical. In the practice the value that can be taken is g= 1.25 But in order not to complicate the calculation formula of dampener size we will use a new constant(0,8) that will give the same result. P2 x dv Vo= -----------------------( 0.8)x0.9x(P2-P1)


Pulsation dampers size calculation - Hidracar

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This formula can be used in practice in all applications needed in the industry. The volume calculated with this formula many times will not be those of one standard manufacturer dampener; except in very exigent applications we can recommend to use the manufacturer standard lower volume, for cost reasons obviously Note: we have not consider a possible temperature variation of the fluid or environment. This will change the charging gas value at 20º (take note that for a 10ºC of temperature variation the gas pressure will change aprox. a 3%) << previous - next >> Políg. Ind. "Les Vives", s/n. - Apdo. 35 - 08295 SANT VICENÇ DE CASTELLET (Barcelona) España Tel.: +34 938330252 - Fax: +34 938331950 - [email protected] - aviso legal - © 2006 Hidracar.com


Pumps types for mounting pulsation dampers - Hidracar

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Pumps types for mounting pulsation dampers We will consider the pumps of one, two or three pistons with crankshaft movement because are the more extended and used and also those that need the dampeners more(for air operated , peristaltic, etc pumps consult the HIDRACAR SA technical department). The graphics that we will see below corresponds to this three types of piston pumps and represents the instantaneous flow during a complete crankshaft revolution . We have taken the same piston dimensions (diameter x stroke) for the three types of pumps.

If we make attention to this curves we will see how a pulsation dampener works; let us comment the first curve of a single piston pump : For this type of pump the use of a dampener is quite necessary because during half revolution of the pump this, does not give any quantity of liquid to the circuit. Also if the pump does not have a dampener, the diameter of the pipe must be calculated for the maxi. instantaneous flow, that happens at the piston maxi speed ( in the middle of piston stroke because the curve is a sinusoid curve ). With the dampener installed , from the point where it is mounted the flow supplied to the circuit is the mean flow then the pipe diameter can be reduced by 40% !! and this because the maxi. and this because the maxi. instantaneous flow is 2.8 times superior to the medium flow. In many cases this reduction of pipe diameter will compensate the cost of the dampener. Following the first curve we can see that the dampener stores all the volume over the mean flow line of the total piston head during the impulse piston stroke, and this volume “d1 “ is returned to the circuit during the suction pump stroke. As we can see in this type of pump the volume stored by the dampener is the half of the pump head or capacity per revolution. Analysing the three curves we see that, when the pump increases the number of pistons the mean flow goes near to the maxi flow and the dampener stored liquid “ d1“ is reduced . Another data we can obtain observing the three curves is the flow across the dampener ;this value is reduced when the number of pump pistons are increasing.( that is valid in this case where all the pistons, in the three pumps have the same diameter, stroke and number of revolutions per minute) To summarise ; the more piston’s pump has the lower dampener size is and also lower can be the port connection between the dampener and the circuit The relation between ”dv” and “C” is: ( C = the pump capacity per one revolution ) dv = C / 2 For a one single acting piston pump dv = C / 6 For a two single acting piston pump dv = C / 18 For a three piston pump We know that when a volume of gas is reduced its pressures increase ,and the opposite if the volume expands the pressure decreases .When a dampener is installed in a circuit the pressure will fluctuate according to the values of the volume of gas inside the dampener ; this pressure variability will be defined by the technical designer of the circuit or by final customer requirements The following graphs will help understanding what we have exposed.


Pumps types for mounting pulsation dampers - Hidracar

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The lower curve from the above graphs is those of the circuit pressure with the dampener installed. This curve depends on the flow variation curve. We have seen that the dampener began to store liquid in the short time when the pump flow is higher than the mean flow ,point 1 and at point 2, all the” dv” has been stored into the dampener. For this the pressure curve is going up from 1 to 2. We should remember that the area between the instantaneous flow curve and the abscissa axle, represents a volume, in this case and for a single piston pump is the pump capacity per stroke or per revolution.(flow x time =volume) We are going to see the meaning of P1,Pt, and P2 in the curve of pressure against time In all hydraulic circuits the pressure at the pump outlet port is a function of the flow, length and diameter pipe, viscosity high, internal pipe surface roughness, etc .If the flow is constant along the time , the pressure to pump the liquid will be also constant and that if there is not any variability in the flow resistance (like filters and others, for instance) At this constant pressure we will call “Pt”. When a circuit must be designed, one ought to take the mean flow and the resistances to calculate the pressure “Pt”. We see that from one side the dampener stabilize the flow and for that also the pressure, but in fact the pressure goes from P1 to P2. This contradiction is because the dampener has to regulate the flow and for that it needs to compress and expand a gas, and this pressure variations are those that regulate the values accepted for the circuit. We already have seen that this pressure oscillations can be reduced up to very small values but for that the dampener will increase its volume.”P1” and “P2” are the percentage values of “Pt” that we have already commented before. << Previous - Next >> Políg. Ind. "Les Vives", s/n. - Apdo. 35 - 08295 SANT VICENÇ DE CASTELLET (Barcelona) España Tel.: +34 938330252 - Fax: +34 938331950 - [email protected] - aviso legal - © 2006 Hidracar.com


Pulsation dampers mounting opinions - Hidracar

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Pulsation dampers mounting opinions MOUNTING OPINIONS TO OBTEIN THE MAXIMUM DAMPENER EFFICIENCY The pump who has the higher relation “instant. maxi. Flow/ mean flow” is the one single piston pump, and also the type of pump where “dv” has a higher value ( liquid going into and out of dampener in each cycle). Therefore in the next example we will expose this type of pump. We can say that in 99% of industrial applications if the recommendations that we expose are followed the dampener’s efficiency is guaranteed

1) 2) 3) 4) In

Mounting the dampener with its axle lined with the outlet pump axle The distance between the pump outlet port and the dampener port connection must be as short as possible. The pipe section from the pump to the dampener ought to be calculated for the maxi. pump Instantaneous flow. The pipe section from the dampener to the circuit must be calculated according to the mean flow. the next drawing we will see more clearly all the concepts we have exposed so far.

w = pipe section for the mean flow W=small length of pipe for the maxi. instantaneous flow Q = maxi. Instantaneous flow q = mean flow L = as short as possible distance between pump and dampener

To show the difference between the inline and derivation connection to the circuit we will remember one mechanical fluids concept When a liquid is moving into a tube there are different speed lines .In the centre of the tube the speed is maxi. and near the internal tube wall the speed is nearly zero ( see next drawing) If the liquid mean speed increases, the difference is higher between the dynamical pressure,-the pressure measured in the liquid direction-and the static pressure- the pressure measured perpendicular to the liquid direction-. We can see that the dampener inline mounting corresponds at the measure of the dynamic pressure, and the derivation mounting corresponds to the static pressure.


Pulsation dampers mounting opinions - Hidracar

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If the dampener is mounted in derivation, at a large distance from the pump and besides with a smaller diameter than the main circuit pipe, then, the efficiency of the dampener could be reduced a great deal. << Previous - Next >> Políg. Ind. "Les Vives", s/n. - Apdo. 35 - 08295 SANT VICENÇ DE CASTELLET (Barcelona) España Tel.: +34 938330252 - Fax: +34 938331950 - [email protected] - aviso legal - © 2006 Hidracar.com


Peculiar aplications for the pulsation dampers - Hidracar

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»» products »» pulsation dampers »» technical article »» peculiar aplications for the pulsation dampers

Peculiar aplications for the pulsation dampers I ) CIRCUITS THAT NEED TO BE CLEANED PERIODICALLY AFTER FINISHING EACH PROCESS All the pulsation dampeners whatever was its form and because its own design, they have internal corners which are difficult to clean or to eliminate all particles of the product pumped; of course ones more than others. According to our 26 years of experience the more secure and efficient solution is to use a quick bladder dismantling system from the inside dampener , and clean separately the bladder and the dampener internal body. This solution for applications where the charging gas value is lower than 10 Bar and if the dampener can be filled with compressed air, is the most effective. II) CIRCUITS WHERE THE WORKING PRESSURE CHANGES The Pulsation dampener application in this type of circuits has different solutions. Also in this case the experience has shown us that the best solution is as always, the most simple one ,or at least is the solution that requires lower maintenance, any costs of energy and of course a low price. Lets have an example. A circuit that must work at an initial pressure of 20 Bar and a final pressure of 200Bar The “dv” = 10 c.c. and the residual pulsation accepted, in the case more disadvantage (at 200 bar ) ought to be :+,- 5%. The pump is a single piston type and its capacity per stroke is:20 c.c. To simplify the calculations we will consider that the gas volume variation is at constant temperature isothermal curve where, P x V = Constant From:

PoxVo=P2xV2 ,

Po= 0.9x20= 18 bar ,

P2= 200 + 5%=210 bar

P2/Po = Vo/V2 = 210/18 = 11.66 (8) We will calculate the hypothetical dampener volume for the maxi. pressure of 200 Bar Vo(200) = (10 x 210) / 0.9 x ( 210 - 190 ) = 116,66 c.c. This volume is to be equal to ”V2” from the formula (8), then: ( Vo / 116.6 ) = ( 210 / 18 ) = 11,66

and

Vo = 116,6 x ( 210 / 18 ) = 1360,33 c.c.

this is in theory the total pulsation dampener volume necessary for this application , but the relation , Vo / V2 can not be higher than 4 in order not to corrugate too much the bladder and damage it in a short time. In this case because Vo / V2 is; 1360,33 / 116,66 = 11 nearly 3 times higher than the value of 4 that we recommended. To achieve that the volume bladder does not exceed the relation of 4:1 we will introduce a quantity of liquid inside the bladder mixed with the gas ( usually the same liquid of the circuit or any other which has not any reaction with the bladder material or with the circuit liquid ) The volume to be introduced into the bladder “VL” ( see sketch ) will be calculated ( 1360,3 + VL ) / ( 116,6 + VL ) =< 4 ; and operating , VL = 298 c.c. Then the total dampener volume needed will be:

1360,3 + 298 = 1658,3 c.c.


Peculiar aplications for the pulsation dampers - Hidracar

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<< Previous Políg. Ind. "Les Vives", s/n. - Apdo. 35 - 08295 SANT VICENÇ DE CASTELLET (Barcelona) España Tel.: +34 938330252 - Fax: +34 938331950 - [email protected] - aviso legal - © 2006 Hidracar.com


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