A down-the-hole drill, usually called DTH by most professionals, is basically a jackhammer screwed on the bottom of a drill string. The fast hammer action breaks hard rock into small cuttings and dust that are evacuated by a fluid (air, water or drilling mud). The DTH hammer is one of the fastest ways to drill hard rock. The system is thought to have been invented independently by Stenuick. Origin of the nameDTH is short for “down-the-hole”. Since the DTH method was originally developed to drill large-diameter holes. .
In DTH drilling, the percussion mechanism – commonly called the hammer – is located directly above the drill bit. The drill pipes transmit the necessary feed force and rotation to the hammer and the bit, along with the flui. .
A is first thought to have been used for rock drilling in 1844. Many quarries used hand held tools that required the driller to suspend himself from a rope over the quarry face in order to place the drill hole in.
[pdf] 
First, safely remove the bit from the drill—use a cloth or gloves to avoid direct contact with the overheated metal. Inspect the bit for any visible damage such as discoloration or warping. If the bit appears to be damaged, it’s best to replace it..
First, safely remove the bit from the drill—use a cloth or gloves to avoid direct contact with the overheated metal. Inspect the bit for any visible damage such as discoloration or warping. If the bit appears to be damaged, it’s best to replace it..
Stop Using the Drill: As soon as you notice the drill overheating, stop using it immediately. Continuing to use it can cause damage to the tool and increase safety risks. Disconnect Power: Unplug the drill from the power supply..
Overheating in drills is more serious than it sounds, and you should know the correct ways to fix your tool fast. The easiest and most common ways to cool down the drill include changing the drill bit and lubricating it. It is likely time to change your drill bit when it gets full.
[pdf] 
To take the second part of the question first: most of the time, it doesn’t. The pressure relief valve is a safety valve that protects the compressor component that it’s attached to from being exposed to a pressure above its rated maximum operating pressure. This rating, called the maximum working pressure. .
Before we can talk about how the air pressure relief valve works, we first need to look at how air pressure inside a compressor is managed when everything is running normally.. .
What happens when the pressure relief valve fails depends on whether it fails with the valve open or the valve closed. .
Whether the valve opened because of excessive pressure in the compressor or because the valve is failing, you should have your local air compressor distributor inspect your compressorbefore running it again for two reasons: 1. First, your distributor can. .
The pressure relief valve opening can be either a sign that excessive pressure is building up inside the compressor or a sign of the valve failing.
[pdf] 