Well done to all the Practitioners out there risking their health to protect the public over the level four lock down.

Many things could cause this including:

Blocked strainer (debris blocking one of the valves)
Faulty limiting valve, or even something could be wrong with the shower mixer. Its hard to say unless you get someone to look at it really. Just get a registered plumber in to investigate.

Hello,
During the COVID lockdown, I wasn't sure if I can really get a plumber out, but I have a shower in the upstairs bathroom. The hot water cylinder is the other side of the wall, and normally the water pressure was perfectly fine. However, over the last month or so the cold water pressure has dropped significantly. I have no knowledge of plumbing, so hoping for some guidance here for what to check, etc. The sink taps are excellent pressure in the same bathroom, and the hot water is fine and hot, with moderate pressure. I've taken some shots of the HWC and hope someone could suggest some clues. I did notice my water bills have shot up, though I haven't discovered any leaks anywhere.
Please let me know if there's any information I could provide?
Warm Regards, and stay safe

In times like this recent COVID scare...I just wish I had more confidence, and could place more trust, in those that lead.

 A factory requires water to be supplied that gives a flow rate of 230 litres per minute at a pressure of 750 kPa at the outlets.
The supply pressure is 835 kPa.
Give the minimum diameter of the RPZD that can be installed to meet these requirements.

I know the answer is 64
but is there an equation or formula to find this out

SO WHAT? WHAT IF?  Simple questions which may just help you.

Its troubled times but if we follow the main directive we will survive without confusion.

Nothing is ever 100%. What im suggesting would be the most common reason for what you are describing. The valve should be visible behind the wetback, to be sure, light the fire and watch it to confirm. Also make sure the wetback is open vented (just to be safe).

Hi Plumber

Thank you for that so i assume it is normal then and doesn't pose any danger of blowing the side of my off

Hi Jaune,

It sounds like your wetback has a pulse valve to assist the siphon. When the valve heats up the spring is loaded, at a certain temperature there is a tipping point and the release sounds like a bang.  More details here >> http://www.pulseflow.co.nz/