Diary of an engineer: Valves and schematics

Submitted by AWL on 15 July, 2020 - 7:06 Author: Emma Rickman
Engineering plant

Brace yourself for a pretty technical and nerdy diary entry. One of my tasks this week has been to identify the valves on the plant that will need isolating during the Outage.

Each valve controls the flow of water or steam for a significant process on the plant, and all are operated remotely from the Control Room. I look up “the addresses” for all the valves, then I go in search of the cabinets on the plant itself.

I have to find the actual physical position of each valve, and as I’m doing so pieces of information I’ve picked up slowly during my training start to click into place. Most of the significant valves control the flow of steam in the turbine hall; these are huge red things controlling steam hurtling through pipes as wide as a kitchen table.

On Level 9 I find some valves tucked behind the long horizontal cylinder that is the boiler itself. It’s very hot at this level and I struggle trying to confirm the valve tag-numbers on cables covered in grime. These valves control the flow of steam and feed-water to the boiler and, confusingly, the flow of water to “de-superheat” the steam once it has been through the boiler so that some of it can be condensed and re-heated in the furnace.

The I/O cabinets can be found on different floors of the plant, not necessarily near the valves themselves. Each cabinet has a row of PLC (Portable Logic Control) modules — small blue boxes with lots of holes in them — that transfer instructions to or from the computer to individual signal wires. These signal wires connect to terminal rails, which link to the wires going to the valves or instruments — these are the “field wires”, because they connect devices “out in the field”.

Within the cabinets are dusty folders of schematics which I thumb through by torch light — I find the drawing given by the address in the I/O folder, confirm that the instrument exists in the drawing, and find the terminal where its field wire is located. The schematic drawing shows me the instrument (by tag number) and a line branching off it to connect with a long horizontal line marked “Earth” — this branching line is numbered “3” and the “earth” line is marked “X25”, so to isolate the valve I must disconnect the cables at terminal 3, X25.

I search for some terminals within the cabinet and find them easily. Others, I search several times and don’t trust my senses until I find another bank of terminals hiding behind the cabinet. One of the cabinets is kept underneath the feed-hopper where the waste is dropped into the furnace, and the crashing of waste onto the metal roof above me is deafening.

In other news, we now have a functioning fly-zapping machine in our mess-room (The Insectocutor) but there are still many flies that aren’t buying it.

• Emma Rickman is an engineering apprentice at a Combined Heat and Power plant


Other entries in the “My Life At Work” series, and other workers' diaries

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