This came in the London March 2014 exams and many students struggled to get higher than 6.5. Since there are a lack of resources on the internet to help answer this question, my students have asked me to share this sample answer. Again, I must stress that you have any online sample answers verified and checked by an actual examiner or IELTS trained tutor before studying it. If you’re an IELTS teacher, please remember to teach the language techniques of a process diagram so that they don’t memorise answers.
The diagram below shows how a hot air balloon ascends and descends.
Summarise the information by selecting and reporting the main features and make comparisons where relevant.
(Sample answer 193 words)
The diagrams compares how a hot air balloon is operated in order for it to ascend and descend.
Generally, warmer air causes the balloon to rise whereas cooler air with the help of the parachute valve, will lower it. These actions can be controlled by the pilot situated in the basket of the balloon.
To raise the balloon, the pilot releases gas from the propane tanks located in the basket to flow into the burner which is underneath the skirt of the balloon. This causes the burner to produce a flame which draws heat into the envelope. The pilot does not need to operate the parachute valve at this time. As the air inside the balloon heats up, the gores and panels of the envelope expand, causing the balloon to ascend.
In comparison, to allow the balloon to descend, the pilot must not ignite the burner. Instead, the parachute valve cords are pulled down, causing the parachute valve at the very top of the balloon to open. This forces the hot air inside the envelope to escape so that cooler air can enter, thus lowering the temperature for the balloon to descend.