Can you identify stop tap attachment? (Ed.)

[tinybob421]

I’ve been investigating an issue of low water pressure and was looking at possibly replacing the stop tap.
When having a proper look there is a mystery black object plumbed in above the tap.
Anyone have any clue what it might be?
Thanks for any thoughts

 

[ReganAndCarter]

Looks like a shock arrestor. It's there to dampen the shock of the washing machine fill valve closing suddenly which can cause banging noises throughout the incoming cold supply pipework. The banging caused by water flow stopping suddenly when the w/machine fill valve closes is known as water hammer.

Other valves, usually toilet fill valves/ballcocks, can cause water hammer when they close.

 

[gas112]

yep looks like a shock arrestor

 

[Stuckinarut]

As above, likely a shock arrestor. Regards the low pressure is it everywhere? Do you mean pressure or flow?

 

[Madrab]

might even be a shock arrestor

Give us a side on view but there seems to be an appliance valve behind it.