How can loss of suction in a pump be avoided?

Choosing all measures collectively indicates a comprehensive approach to ensure that a pump maintains its suction and operates correctly. Each method provided contributes uniquely to avoiding the loss of suction, which can lead to cavitation and inefficient pumping.

Using a half tank to keep the pump primed is a practical strategy. By maintaining a sufficient liquid level, the pump can consistently draw in fluid without running the risk of air entering the system, which can disrupt the suction performance.

Opening the vent cock on the pump helps eliminate air pockets in the pump casing or piping, allowing for better fluid flow. This is crucial because any trapped air can hinder the pump's ability to generate the necessary pressure and suction.

Reducing the flow rate is another effective technique. By lowering the demand on the pump, it can maintain suction more effectively, particularly if the initial conditions are leading to a drop in pressure.

Incorporating all these strategies ensures a well-rounded approach to preventing loss of suction, making the selection of 'all of these' the optimal choice.