Posts Tagged ‘positive displacement pump’

A Jelly Depositor is a Positive Displacement Pump

Thursday, June 7th, 2018

    Our last blog introduced a project I oversaw while acting as a design engineer in a food manufacturing plant.   The objective was to deposit fruit jelly into raw pastry dough as it whizzed along a production line conveyor belt before being sent off for baking.   A special piece of equipment known as a depositor would be required to meet this challenge, and we’ll take a look at how one functions today.   In fact, a jelly depositor acts very much as a human heart, as they’re both examples of positive displacement pumps.

    A depositor is a device specifically made for the food industry.   It consists of a hopper to hold the product to be deposited, in this case fruit jelly, which is discharged by the hopper into a rotating diverter valve and then on to a positive displacement piston pump.   See below.

A Jelly Depositor is a Positive Displacement Pump

A Jelly Depositor is a Positive Displacement Pump

   

    When the diverter valve rotates, a passageway opens to allow jelly to flow from the hopper into the piston pump.   A pneumatic actuator, a device we’ll discuss in more depth next time, moves the pump’s piston to the left, away from the diverter valve, which allows the filling to be released into the pump from the hopper.   At the end of the piston’s travel a set quantity of fruit jelly filling is drawn into the pump’s housing, just enough to fill one pastry. See below.

The Depositor Draws Filling Into The Pump

The Depositor Draws Filling Into The Pump

   

    When the diverter valve rotates in the opposite direction, a passageway opens inside the valve that allows jelly filling to move from the pump to the nozzle.   As the piston moves back toward the diverter valve the filling is forced out of the pump, through the nozzle, and into the pastry dough.   The pump’s piston moves back and forth, that is, away from and then towards the transfer valve, ushering a set quantity of jelly filling through the mechanism each time.   See below.

The Depositor Deposits The Filling

The Depositor Deposits The Filling

   

    Now that we know how the depositor works, next time we’ll discuss the pneumatic actuator’s role in the filling process.

Copyright 2018 – Philip J. O’Keefe, PE

Engineering Expert Witness Blog

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Positive Displacement Pumps Are Used in Industry

Tuesday, May 29th, 2018

    Last time we learned that the human heart functions as the greatest of all positive displacement pumps, moving a set quantity of blood through it at precise intervals during its operating cycle.   Today we’ll begin our exploration into how positive displacement pumps are used in industry, specifically within a food manufacturing plant.

    At one point in my career I was employed as a design engineer in a food manufacturing plant.   The plant was owned by the leading manufacturer of bakery products in the United States, responsible for supplying restaurants, bakeries, and grocery stores with finished and partially finished pastry goods that they would then resell.   The plant produced vast amounts of puff pastry dough products, all of which were formed and filled with various fillings while zipping along on a production line conveyor belt.   One of the products was a fruit filled pastry in which the belt moved so quickly, depositing fruit fillings into the dough by hand would be impossible, resulting in a frenzied mess similar to what Lucy encountered when she worked in a candy factory.

    Clearly, an automated machine would work better in this and other scenarios.   We’ll see how one known as a depositor functions on a food pastry line next time.

Copyright 2018 – Philip J. O’Keefe, PE

Engineering Expert Witness Blog

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Master of All Pumps, the Human Heart

Monday, May 21st, 2018

    We couldn’t do without pumps. They serve up water from the tap, circulate our car’s coolant, and the master of all pumps, the human heart, keeps us alive.   Pumps are essential in countless areas of our lives, and they’re of two major types, positive displacement or centrifugal.   We’ll start our discussion with a focus on positive displacement pumps.   Our hearts belong to this category.

Master of All Pumps, the Human Heart

Master of All Pumps, the Human Heart

As their name implies, positive displacement pumps displace, that is to say they move or circulate, a set quantity of liquid with each operating cycle.   Your heart moves 2 to 3 ounces of blood with every heartbeat and up to 2,000 gallons of blood per day!

Next week we’ll introduce an industrial application for a positive displacement pump when we install one in a food manufacturing plant.   You didn’t think those jelly pastries filled themselves, did you?

Copyright 2018 – Philip J. O’Keefe, PE

Engineering Expert Witness Blog

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A Pump By Any Other Name…

Monday, May 10th, 2010

     Pumps are all around us.  They keep our drinking water flowing, the cooling water circulating in your car’s engine, and even your blood flowing.  They’re essential in many aspects of our lives, but most of us don’t think too much about them.  For our discussion let’s put them into two categories:  positive displacement pumps and centrifugal pumps.  This week, we’ll focus on positive displacement pumps.

     Positive displacement pumps, as their name implies, displace a quantity of liquid with each complete cycle of movement.  This takes place when moving parts of the pump take “bites” out of the liquid at the inlet, then force them to exit through the outlet.  A familiar example of a positive displacement pump is the type of hand operated water pump that’s commonly found in campgrounds.  See Figure 1.

 

Figure 1 – A Positive Displacement Pump

     This type of pump is known as a reciprocating positive displacement pump.  By reciprocating, I mean that the moving parts travel back and forth in a straight line during its operation.  Let’s see how it works by referring to the cutaway view in Figure 2.  

 

Figure 2 – Cutaway View of the Pump Shown in Figure 1 

     In the cutaway view, the pump’s piston and internal check valve are shown, and there’s another check valve in the bottom of the pump housing.  When you pull up on the handle, the piston moves down into the water in the pump housing, and the pressure caused by this movement forces the check valve in the bottom to slam closed, while the check valve above is forced open.  This causes water movement to flood through the open check valve and fill up the space above the piston.  When you push down on the handle, the opposite happens.  The piston is made to move upward.  The upward acceleration of the water above the piston causes the check valve on the piston to slam shut, and this traps the water above it.  As the piston moves back up, a suction is created below, which causes the check valve in the bottom of the housing to pop open and more water is drawn up into the space below the piston.  Eventually, when the piston gets high enough, the water trapped on top of it will flow out of the spigot.

    Another type of positive displacement pump is represented by a rotary pump.  These pumps operate in a circular motion to move a volume of liquid with each revolution of the pump shaft.  This is done by trapping liquid between moving parts, such as gears, lobes, vanes, or screws, and the stationary pump housing itself.  

     To show how this works, refer to the gear pump shown in Figure 3.  Its gear teeth mesh together in the middle of the pump, blocking the flow from going straight through and trapping it within the spaces formed by rotating gear teeth and the pump housing.  It’s like the water is being forced through a turnstile.

Figure 3 – A Cutaway View of a Gear Pump

 
     Next week, we’ll talk about centrifugal pumps and how they move liquids along using centrifugal force.
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