fixed displacement balanced vane pump

FIXED DISPLACEMENT BALANCED VANE PUMP

1. Construction and Operation

Unlike in unbalanced vane pump, the balanced vane pump has two intake and two outlet ports which are diametrically opposite to each other. Also a balanced vane pump has an elliptical housing instead of a circular cam ring. This configuration creates two diametrically-opposed volumes. The two high-pressure zones balance the forces on the rotor shaft and hence a complete hydraulic balance is achieved.

Fig.4.13 illustrates the operation of a balanced vane pump. Except the above said differences, the construction and basic working principle are similar to the unbalanced vane pumps.

2. Advantages and Disadvantages of Balanced Vane Pumps (Over Unbalanced Vane Pumps)

Table 4.6 presents the merits and demerits of balanced vane pumps over unbalanced vane pumps.

Table 4.6. Advantages and disadvantages of balanced vane pumps

Advantages

(i) The balanced design of pump eliminates the bearing side loads and thus permits higher operating pressures.

(ii) The balanced vane pumps have much improved service lives over simpler unbalanced vane pumps.

Disadvantages

(i) Balanced vane pumps are necessarily fixed displacement machines. Therefore the displacement of pumps cannot be varied.

(ii) Due to its symmetrical construction, balanced vane pumps are difficult to design as variable displacement pumps,

3. Advantages and Disadvantages of Vane Pumps

Table 4.7 summarises the merits and demerits of employing vane pumps. 

Table 4.7. Advantages and disadvantages of vane pumps

Advantages

(i) Vane pumps are self-priming, robust, and give constant delivery for a set rotor speed. 

(ii) They produce uniform discharge with negligible pulsations.

(iii) Their vanes are self-compensating for wear and also vanes can be easily replaced. 

(iv) These pumps do not require check valves. 

(v) They can pump in either direction.

(vi) They require little space.

(vii) They are light in weight.

(viii) They can handle liquids containing vapours and gases.

(ix) Volumetric and overall efficiencies are relatively high.

(x) Only small changes in capacity occur with variations in viscosity and discharge pressure.

Disadvantages

(i) Vane pumps cannot be operated against a closed discharge without damage to the pump. Hence relief valves are required. 

(ii) They cannot handle abrasive liquids.

(iii) They require seals. 

(iv) Foreign bodies can damage the pump.

4. Ranges of Vane Pumps

Vane pumps are available with capacities upto 125 Lps and the discharge pressures upto 175 bar. Also these pumps can operate at speeds upto 2000 rpm.