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

 

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.

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.

 

 

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