By my observation, the most common hydraulic test cap is the green nut-operated type, but there are a few more types of cap.
red Round Head 30135 with green nut-operated hydraulic test cap on one of its side nozzles
Shau Kei Wan Main Street East opposite Shau Kei Wan Market Building
Photo taken in Y2026-M02
red Round Head 31082 with red hydraulic test cap with handles on one of its side nozzles; the cable from the cap to the hydraulic test box was disconnected for some reason
Chai Wan Road near A Kung Ngam Road bus stop
Photo taken in Y2026-M08
red Round Head 1421 with Vernon Morris Utility Solutions hydraulic test cap on one of its side nozzles
Sing Woo Road opposite of Shing Ping Street
Photo taken in Y2026-M04
yellow Round Head 27530 with rusty hydraulic test cap with handles on one of its side nozzles
Portland Street near Waterloo Road
Photo taken in Y2026-M04
I also found two Round Heads with different hydraulic test cap on the side nozzles...for some reason. One of them is numbered 1716, I'm not sure about the other one.
red Round Head
Photo taken in Y2026-M09
Connected to portable meters
I am not sure what kind of tests are being conductede, but presumably these are equipment are used for tests similar to hydraulic tests.
red Round Head 28528 (previously 1449) with portable meter (?) and tap connected to one of its side nozzles
Waterloo Road opposite of Essex Crescent
Photo taken in Y2026-M04
red Round Head 3258 with portable meter (?) and water tap on one of its side nozzles, but the portable meter (?) was covered and the emergency repair in progress sign was hanged on the attachment
Battery Street at Yau Ma Tei Orthodontic Clinic
Photo taken in Y2026-M04
red Round Head 8840 with portable meter connected to one of its side nozzles
cycling track next to So Kwun Po Road near Kockey Club Road
Photo taken in Y2026-M07
Taps for temporary water supply
When fresh water supply is disrupted in buildings, you might see these taps attached to one of the side nozzles of fresh water hydrants on the street, allowing the affected residents to get fresh water with containers like buckets.
red Round Head 2355 with temporary fresh water supply tap on one of its side nozzles
Eastern Street at Queen's Road West
Photo taken in Y2026-M09
red Round Head 27206 with temporary fresh water supply tap on one of its side nozzles
Tung Kun Street Reclamation Street
Photo taken in Y2026-M06
Hoses connecting hydrants to small work sites
Occasionally, you might see hydrants being connected to work sites by hoses.
red Round Head 5895 (later 23251) with hose connected to one of its side nozzles, the hose was connected to a small work site of footbridge lift N546B approximately 150 metres away
Wing Shun Street opposite of Wing Tak Street
Photo taken in Y2022-M01
red Swan Neck 13617 with hose connected to one of its side nozzles, presumably for the footbridge lift construction site next to the Swan Neck
Boundary Street @ Embankment Road
Photo taken in Y2026-M04
A red unnumbered Swan Neck with hose connected to its only outlet nozzle, presumably for the water works site next to the Swan Neck
Garden Road @ Queen's Road Central
Photo taken in Y2026-M07
Pipes for big work sites
On Pak Shing Kok Road, Round head 6640 had a big pipe connected to its front nozzle. From Google Maps street view, we can see that the pipe goes into a big work site nearby, known as the "Site Formation and Infrastructure Works at Tseung Kwan O - Yau Yue Wan and Pak Shing Kok". This started happening at some point between Y2022-M02 and Y2023-M06, and is still ongoing as of Y2026-M05.
red Round Head 6640 with a pipe connected to its front nozzle
Pak Shing Kok Road, approximate 100 metres south of the Fire and Ambulance Services Academy Citybus stop
Photo taken in Y2026-M05
Fixed pipe that leads into the ground
On Robinson Road opposite of the Ying Wa Girls' School bus stop, there is a Round Head with a pipe attached to one of its side nozzles. Unlike the temporary appearance of the other setups I have discussed in this page so far, this setup looks much more "fixed". It was already like that in Y2009-M07 (the earliest Google Maps street view capture of the location). I have no idea where the water is being transported to via that pipe, and for what reason.
red Round Head 30681 (previously 2111), with a pipe connected to one of its side nozzles, the pipe leads into the ground
Robinson Road opposite of the Ying Wa Girls' School bus stop
