Cam actuated rotary pump

International Journal For Research & Development in Technology
Volume: 2, Issue: 1, JULY-2014 ISSN (Online):- 2349-3585
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Copyright 2014- IJRDT www.ijrdt.org
CAM ACTUATED ROTARY PUMP
Aravind S1,Aswin Raj. M.2, C R Rahul3,
Dileep S4, Nandu S5
12345 Department Of Mechanical Engineering,
Saintgits College of Engineering, Kottayam,Kerala.
Abstract- The aim of this project is to design a positive displacement rotary pump for small scale applications. The design is in such a way that it combines the advantages of both rotodynamic and positive displacement pumps. Currently available centrifugal pumps cannot attain high heads, and reciprocating pumps are less efficient and requires much space. When centrifugal pump is used as a jet pump, it delivers fluids at a high head, but in the expense of efficiency.
To overcome these negatives of currently available pumps, a new design of a rotary type positive displacement pump is developed. This design imitates the working of a normal reciprocating pump, but in a rotary action. This consumes less space compared to a reciprocating pump of same capacity. The main part of the pump is a cam which is mounted on a rotating shaft that rotates in a cylindrical casing. The cam is designed in such a way that it always maintains contact with the walls of the casing as it rotates. A spring loaded blade acts as the cam follower and moves in an accurately machined slot in the casing. The blade and the slot are of rectangular cross section. This blade separates suction and delivery sides of the pump. Inlet and outlet ports are placed on either sides of this blade. This pump does not require inlet and outlet valves. The discharge from the pump is continuous. It also eliminates the crank and connecting- rod mechanisms and delivers a smooth operation.
Keyword:- Rotary Pump, Rotating Shaft, Cam, Follower blade. I.INTRODUCTION
Pumps are hydraulic machines which convert mechanical energy into hydraulic energy. Pumps operate by some mechanism (typically reciprocating or rotary), and consume energy to perform mechanical work by moving the fluid. Pumps operate via many energy sources, including manual operation, electricity, engines, or wind power, come in many sizes, from microscopic for use in medical applications to large industrial applications.
Mechanical pumps serve in a wide range of applications such as pumping water from wells, aquarium filtering, pond filtering and aeration, in the automobile industry for water cooling and fuel injection, in the energy sector for pumping oil and natural gas or for operating cooling towers. Centrifugal pumps are widely being used in house hold applications where
low heads are required. These pumps deliver fluids at a constant rate. These are very compact and require less maintenance. But for applications where high heads are required centrifugal pumps are inadequate. Modifying a
centrifugal pump as a jet pump enables pumping at high head, but at the cost of efficiency.
Reciprocating pumps are well known for their ability to achieve very high head. But the discharge from such pumps is pulsating. Reciprocating pumps occupy large floor space as the number of components is more. The initial cost is high and requires high maintenance. So their application is mainly confined to industrial fields.
The prime objective of this project is to develop a rotary type positive displacement pump which can be used to pump fluids at relatively higher heads. The design is focussed in reducing the number of parts and in turn the overall size. It also aims at smooth running and constant delivery of fluid. For use in household applications, the pump should operate with minimum noise and vibration levels. There should be minimum maintenance requirements also. A positive displacement pump can attain high heads while the rotary operation leads to smooth noiseless operation.
II. DESIGN APPROACH
A. Power requirements
For starting the design process, it is necessary to set some required output parameters. An ordinary household centrifugal pump used to pump water from well was used for comparison. The specifications of the pump were obtained from the name plate. The driving motor was of rated power 373 W, and the flow rate indicated was 0.0007 m3 per second. The maximum head attainable was 12 meters of water. So the desired head was set as 12 meters and flow rate as 0.0007 m3/s of water. These values are used in calculating the power required to pump water.
Required head = 12 m.
Required discharge = 0.7 x 10-3 m3 / s
Power required for pumping (theoretical)
Ppumping = ρgHQ
= 1000 x 9.81 x 12 x 0.7 x 10-3
= 82.404 W
This is the theoretical power required in pumping water for above mentioned head and discharge. But a machine cannot be 100% efficient. So the actual value of input power required will always be greater than theoretically calculated value. Thus efficiency factor comes into play.
Assuming pump efficiency as 25%
Power, P = Ppumping ηpump

Paper Title:- Cam Actuated Rotary Pump (Vol.2,Issue-1) ISSN(O):- 2349-3585
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= 82.404 0.25 = 329.616 W So, a commercially available motor of (0.5 hp) 373 W was selected to drive the pump shaft. The motor works on AC supply. A single phase motor was selected because a three phase supply is not available everywhere. B. Speed calculations Calculating the power required is not sufficient in selecting the driving motor. Speed of the pump shaft is necessary in determining the type of motor required. Since this is a positive displacement pump, required speed of the shaft can be directly obtained from required flow rate. But it is necessary to set some dimensions arbitrarily to start with. Some of the dimensions were set and used in the following calculation. Those dimensions are described in the following chapters. The swept volume in one revolution of shaft was calculated using software. Swept volume for 1 revolution of shaft, V = 0.000044178 m3 Discharge, Q = V x N60 Speed, N = Q x 60 V = 0.0007 x 600.000044178 = 950 rpm ≈ 960 rpm C. Design of belt drive Shaft speed required was calculated in the previous section. But the problem was that, a low cost motor running on AC supply at 960 rpm was difficult to find in market. So, an easily available, 0.5 hp (373 W) motor running at 1440 rpm was selected and bought. To reduce this speed from 1440 rpm to 960 rpm, the use of a suitable reduction mechanism became necessary. Considering low cost and other factors, v-belt and pulley mechanism was adopted. The design of belt drive (figure 3.1) is carried out below. Driver shaft speed, N1 = 1440 rpm Driven shaft speed requirement, N2 = 960 rpm Driver pulley diameter, d = 0.0508 m Driver ratio = dD = N2 N1 = 9601440 = 0.6666 Driven pulley diameter, D = d0.666 = 0.05080.666 = 0.0762 m Radius of driver pulley, r = d2 = 0.05082 = 0.0254 m Radius of driven pulley, R = D2 = 0.07622 = 0.0381 m Thus the dimensions of the driven and driver pulleys were calculated. Now the dimensions of the belt have to be found out. Calculations are as follows: Angle α = sin-1 (R-r) C = sin-1 (0.0381-0.0254) 0.15 C is the center distance = 0.15 m α = 4.85 deg = 0.084 rad Length of the belt, L = π (R+r) + 2 α (R-r) + 2 C cos α = π(0.0381+0.0254) +2 x 0.084(0.0381- 0.0254)+2 x 0.15x cos (4.85) = 0.4986 m ≈ 0.50 m For designing shaft of the pump, the loads acting on the shaft needs to be calculated. On mounting pulleys on the shaft, it is subjected to a torque and bending moment due to belt tensions. Calculations are as follows: Ratio of belt forces, T1 T2 = eμ’θ Smallest wrap angle θ = 180 - 2α = 180 - (2 x 4.85) = 170.3 deg = 2.97 rad μ’ = effective friction coefficient = 휇 sin β 2 β = pulley groove angle = 40 deg μ = coefficient of friction = 0.3 μ’ = 0.3sin 402 = 0.877 T1T2 = eμ’θ = e0.877*2.89 = 12.61 Torque transmitted to driven shaft = Torque transmitted by the driver x Dd Torque, T = P x 602π N1 x 32 = 373 x 60 2 π x 1440 x 32 = 3.71 Nm T1 - T2 = 3.71R = 3.713.81 x 10-2 = 97.37 N Therefore, T1 = 105.75 N T2 = 8.38 N Shaft load, F = T1 cos(α) + T2 cos(α) = 105.75 cos (4.85) + 8.38 cos (4.85) = 113.72 N D. Design of shaft

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It is already seen that the pump shaft is subjected to a turning moment as well as a bending moment. The magnitudes of the same have been found out in the previous section. Using those values the design of the shaft is carried out. Using maximum shear stress theory: Π16 x Гmax x ds3 = (M2 + T2) ds= Diameter of the shaft T = Torque transmitted = 3.71 Nm M = Bending moment acting on shaft. = F x (Overhanging length) = 113.72 x 40 x 10-3 = 4.54 Nm Assume Гmax = 56 MPa On solving for ds: ds = 0.00810 m ≈ 0.010 m Thus the designing of all required components has been carried out. The loads acting were calculated and applied in finding out the safe dimensions of all key parts. III. COMPONENT DESCRIPTION A. Cam The main component of the pump is a cam (Fig. 5.1). The design aspects of the cam were calculated. The design of the cam is in such a way that it always maintains the contact with the walls of the cylindrical casing as it rotates. There is a provision provided on the cam to insert the shaft onto it. The cam is mounted on the rotating shaft which rotates inside the casing.
Fig. 1. Cam The rotation of the cam inside the casing creates the vacuum which leads to the suction of fluid into the pump casing. The cam was casted in aluminium. The material selection for the cam was made aluminium in order to reduce the weight. B. Cylindrical casing The engine sleeve is selected as the casing for the cam inside which it provides a smooth rotation. In order to provide adequate strength to the engine sleeve a Galvanized Iron pipe is used as the outer casing. The GI pipe was made tight fit with the engine sleeve.
The assembly of the engine sleeve and the GI pipe was turned in lathe to required dimensions (Fig. 2). The casing has an inner diameter of casing 70 mm and length of the casing is 36 mm. The inlet and outlet ports were drilled on the periphery of the casing.
Fig. 2. Cylindrical casing A rectangular slot was also made on the periphery of casing in order to enable the movement of the follower blade. This slot should keep tight tolerances for the sliding movement of the rectangular blade otherwise there will be excessive leakage. C. Blade
Fig. 3 Follower blade The blade (Fig. 3) is a component that separates the suction and delivery side of the pump. The blade too was made from aluminium, in order to reduce the wear as it is always in contact with the rotating cam. The blade has a rectangular cross section of length 80 mm, width 30 mm and thickness 6 mm as its dimensions. The blade reciprocates in the slot provided on the casing. D. Side walls It is made of mild steel plate. It was turned in the stepped form and made tight fit with the casing (Fig. 4). It has a step thickness of 3mm and stepped portion has a diameter of 70mm, with outer diameter 76mm. The two side walls provide air tight chamber in the casing. It also houses the seat for the two bearings.

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Fig. 4. Side walls E. Motor A single phase AC induction motor (Fig. 5) is used to impart power to the motor shaft. Power rating of the motor is 5 HP (0.37kW) at 1440 rpm.
Fig. 5. Driving motor IV. WORKING This section explains the working principle of the pump. The following figures show how the fluid is sucked into the cavity and how it is pumped out to a higher level. As from the Fig. 6 (a) below, the water is sucked in during the counter clockwise rotation of the cam. This is due to the fact that the volume of the cavity keeps on increasing with the counter clockwise rotation of the cam creating a vacuum pressure inside the cavity. In the Fig. 6 (b) the apex of the cam is at top, displacing the follower blade to maximum. At current position, the whole cavity is filled completely by water. Now suction process is complete. In the last Fig.6 (c), further advancement of the cam anti clockwise pushes the water out via the outlet port, which is connected to the delivery pipe. Again, this cycle continues and water gets pumped continuously. This is the basic working principle behind the cam actuated rotary pump. The rate of discharge depends upon the speed of rotation of the shaft.
(a)
(b)
(c) Fig. 6. Working principle V. RESULTS AND DISCUSSIONS A cam actuated positive displacement pump is designed and fabricated. The pump operates smoothly. It has less noise and vibration. The delivery is at a constant rate. The suction and discharge happens simultaneously. The absence of unidirectional valves and other linkages like crank and connecting rods reduce the complexity and floor space required.

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The pump was tested for measuring actual discharge and head developed. A pressure gauge of range 0-7 kg/cm2 was mounted on the delivery pipe. A 0.3 m x 0.3 m measuring tank was used to measure actual discharge. Pump was coupled to electric motor through v-belts and pulleys. Motor was run at rated speed and rise in water level was noted. Maximum pressure developed was obtained from pressure gauge reading. Observations were used for evaluation of performance. Performance curves were plotted and explained below.
Fig. 7. Flow rate vs Head The discharge was found to be decreasing with increase of head (Fig. 7). This is mainly due to the increase of leakage around the cam with increase in pressure. The tolerances are not close enough to seal the leakages. There is excessive leakage through the rectangular groove provided for the movement of the follower blade, at high pressures.
Fig. 8. Output power vs Head Output power Vs head developed shows that output power first increases, and then decreases with increasing head (Fig. 8). This is because initially, drop in discharge with increasing head is gradual. After that the discharge drops steeply.
Fig. 9. Volumetric efficiency vs Head The volumetric efficiency vs head curve (Fig. 9) follows the same pattern as that of flow rate vs head. The reasons behind this nature are already explained earlier. Further increasing of pressure was not carried out during testing because leakage was much higher and discharge was very small. Finally, from above findings it was observed that the prototype of the pump could achieve a maximum head of 5.5 meters of water and delivery of water at a maximum rate of 0.27 litres of water. The peak volumetric efficiency obtained was 38.5 %. The performance curves were plotted and were discussed. The results are concluded, in the next section. VI.CONCLUSIONS A new type of positive displacement pump was developed, which does not require inlet and outlet valves. The discharge from the pump is continuous. It also eliminates the crank and connecting-rod mechanisms. This has the advantages of continuous delivery of fluid, smooth and noiseless operation and compact size. The expectations were that the new design can develop high heads without much variation in flow rate. But it did not develop head as expected and discharge was dropping rapidly with increase of pressure. The main reason behind this is excessive leakage past the seals. There was leakage through sides of the cam and also through the rectangular slot provided on the cylindrical casing for the sliding of the follower blade. But if close tolerances are kept, this pump can work as expected. It should be also noted that this type of pump will be more suitable in pumping of viscous fluids, where effect of sealing problems can be reduced to some extent. From performance curves, the observed trends were similar to the usual trends of most of the positive displacement pumps. As expected, the discharge as well as volumetric efficiency dropped with increase in head. REFERENCES [1] Burkhard Verhuelsdonk, 2005, “Increasing the operational lifetime of rotary lobe pumps”, World Pumps, September 2005.
[2] Hua Yang et al., 2011, “Study on leakage via the radial clearance in a novel synchronal rotary
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refrigeration compressor”, International Journal of Refrigeration, Vol. 34. [3] K.T. Ooi, 2005, “Design optimization of a rolling piston compressor for refrigerators”, Applied Thermal Engineering Vol.25, 813-829. [4] MelihOkur , 2011, “Experimental investigation of hinged and spring loaded rolling piston compressors pertaining to a turbo rotary engine”, Applied Thermal Engineering Vol.31, 1031-1038. [5] Dr. R K Bansal, 2010, “A Text Book of Fluid Mechanics and Hydraulic Machines ”, Revised 9th edition, 993-997. [6] R S Khurmi, 2005, “A Text Book of Machine Design”, Fourteenth edition, 509-714.

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