Various firms as self-priming pumps have patented by various firms as self priming pumps. However, the universally accepted self-priming pumps are:
- Lateral / Side channel pumps
- Ring / Vacuum pumps
Lateral Channel Self Priming Pumps
The pumps consists of an impeller which rotates between two side plates; one of suction side containing suction port and the other on delivery side containing delivery port. In addition to these ports each plate also has a grooved channel near its outer circumference. This channel extends to almost 360 degree (about 330 degree) and is tapered at ends. The impeller is provided with straight radial blades.
Priming and air separation with in casing shells of Self Priming pumps
With just an initial charge of liquid in the casing, the dual volute configuration primes suction. The lower volute serves as an intake during the priming stage, while the upper volute discharges liquid and entrained air into the separation chamber. Through pump discharge, air is separated and expelled, while liquid is recirculated into the lower volute. The pump is fully primed and acts like a traditional centrifugal pump with both volutes acting as discharges until air is entirely separated from the suction and liquid fills the impeller eye.
The interface was developed to still retain a sufficient quantity of liquid in the pump for re-priming. Since the liquid can drain back from discharge and suction to the source of supply.
Working of Lateral Channel Self Priming Pumps
For the first time operation, it will be necessary to fill up the impeller with the liquid to be pumped. For subsequent operation it will automatically prime itself.
Since both the suction and delivery pipes extend vertically upwards from pump, some liquid will be left over in pump chamber when the pump is stopped. On restarting the pump, this liquid is carried by the impeller to lateral channel and delivery pipe and pump will suck air from suction side pipe.
Since the pressure developed by air is negligible, the liquid being heavier returns back from the channel into space between the blades and is now pumped again along with air to the channel and the delivery side. The air is thus expelled to delivery port and the liquid will return to get mixed with freshly sucked in air, which again in turn is expelled. Cycle thus continues till all the air is expelled and the pump develops sufficient head to discharge to liquid. The liquid rotating with the impeller forms a seal between to suction and delivery spaces.
These pumps are made as single and multi stage pumps with discharge up to a maximum of 36 m3/hr. Their efficiency is rather low in the order of 20 to 25%.
Lateral Channel Self Priming Pumps Specifications
- Casing: Grey cast iron
- Maximum operating pressure: 86 psi
- Impeller shaft: Alloy steel
- Shaft sleeve: Alloy steel
- Replaceable Wear plate: Carbon steel
- Cover plate: Grey cast iron (Removable and adjustable)
- Flap valve: Neoprene Nylon with Steel reinforced
- Seal plate: Grey cast iron
- Bearing Housing: Grey cast iron
- Radial Bearing: Open single row ball bearing
- Thrust Bearing: Open Double row ball bearing
- Bearing and Self Cavity Lubrication: SAE 30 Non-Detergent oil
- Flanges: Grey cast iron
- Gaskets: Synthetic fibers
- O-Rings: Synthetic fibers
- Semi open type
- Two vane impeller and made of Ductile iron
Characteristics of Lateral Channel Self Priming Pumps
The Q-H characteristics runs in a familiar way like ordinary centrifugal pumps and so also η curve.
However, power discharge curve shows large consumption and energy initially at zero or low discharge and reaches to minimum value at a point near the maximum efficiency.
Lateral Channel Self Priming Pumps vs Centrifugal Pumps
This style of pump varies from a conventional centrifugal pump in that it has a built-in water reservoir that allows it to relieve the pump and suction line of air during the priming period by recirculating water inside the pump. This water source may be in front of or above the impeller. In this case, the pump’s “self-priming” ability lies in its potential to absorb water after the initial prime.