Every skid, well head and chemical line we touch is controlled by valves, and each style exists because it does one job well and another job badly. This covers the six you handle most: gate, globe, needle, ball, butterfly and diaphragm. For each one: what is moving inside, what it is good for, where you will find it on our systems, and the mistake that shortens its life.
Open. Full, straight bore with nothing in the way, so almost no pressure drop. This is an isolation valve, full stop.
Open. The gap between disc and seat sets the flow. Half a turn changes it a little, predictably. That is the whole point.
Open. The taper means each turn uncovers only a sliver more orifice. Built for fine adjustment of small flows, not for moving water.
Open. Full-port ball: the bore is the same size as the pipe. Fast, tight shutoff, and you can read its state from across the room.
Open. Disc sits edge-on to the flow. Water passes either side of it, so it is never truly full-port, but on a 6 in. main that costs almost nothing.
Open. Nothing metal touches the water. The wetted path is body liner and membrane only, which is why it lives on our chemical lines.
Narrated overview of this module. The article below has the full procedure and the numbers.
Every valve is asked to do one of two things: isolate (fully on or fully off) or throttle (hold a partial position to regulate flow or pressure). A valve designed for isolation gets chewed up when left half open. A valve designed for throttling adds pressure drop even when wide open. Nearly every valve failure we replace traces back to the wrong type doing the wrong job, or the right type left in the wrong position.
A flat or wedge-shaped gate rises out of the flow path into the bonnet, or drops across it. Wide open, the bore is unobstructed and pressure drop is close to a straight pipe. Closing takes many turns of the handwheel, which is deliberate: on a large main, slamming the flow shut would hammer the line.
Isolation on larger lines where head loss matters and you rarely operate it: well head discharge, raw water mains, municipal plant piping, big tank inlets. Cheap per inch of pipe at 3 in. and up.
Well sites and municipal BWRO feed, tank farm isolation, older commercial mechanical rooms. Rising-stem versions show position by how much stem is exposed; non-rising stems do not, so you turn until it stops.
If a gate valve will not fully close, do not force the handwheel. Back it open a turn, let debris flush through, and try again. Forcing bends the stem and you now own a bigger problem.
Flow enters, turns up through a seat ring, passes under a disc and turns back down. The disc travels straight toward the seat, so the opening changes smoothly and repeatably with each turn. That S-shaped path is what makes it a control valve, and it is also why a wide-open globe still costs you several feet of head.
Anything you set and leave at a partial position: RO concentrate (reject) control on commercial and industrial skids, pump discharge throttling to hit a design flow, recirculation and blend lines. It holds a setting under pressure without creeping.
The concentrate valve on most AXEON and custom RO skids, boiler and cooling tower feed, hot water recirc balancing. Many are direction-sensitive: find the flow arrow on the body before you install.
When you set RO recovery with the concentrate globe valve, record the number of turns from closed. The next tech can return to the setpoint without a flow meter in hand. See the RO recovery article.
A globe valve shrunk down and fitted with a long tapered pin in place of the disc. The pin threads into a small orifice, so a full turn changes the opening by a tiny amount. It gives you precise, repeatable control of small flows and pressures, and it is nearly useless for anything else.
Fine adjustment where a fraction of a GPM or a few PSI matters: gauge snubbers and isolation, sample ports, pilot and sensing lines, chemical injection tuning, and the concentrate control on small residential and light-commercial RO units.
Stainless needle valves feeding pressure gauges and sample taps on skids, brass ones on residential RO manifolds, small chemical feed lines ahead of the injection quill.
A needle valve on a gauge line does two jobs: it isolates the gauge for replacement, and cracked barely open it dampens pulsation from a positive-displacement pump so the needle stops bouncing.
A ball with a hole bored through it sits between two seats. A quarter turn of the handle lines the bore up with the pipe or turns it broadside to stop flow. Fast, positive shutoff, minimal pressure drop in full-port versions, and the handle tells you the valve state at a glance: parallel to the pipe is open.
Isolation you operate often and need to trust: softener bypass, tank inlet and drain, skid inlet and outlet, sample taps, chemical drum quick-disconnects. Sch 80 PVC true-union ball valves are the workhorse on our skids because you can service the ball without cutting pipe.
Everywhere. Bypass assemblies on every softener and filter we install, tank drains, RO skid isolation, pretreatment manifolds, hose bibs and sample ports on plant piping.
A closed ball valve traps fluid in the body cavity. On a chemical line, that pocket of bleach or acid is still there when you break the union. Relieve pressure and open the drain side before you disconnect.
A flat disc mounted on a shaft that runs straight through the center of the bore. A quarter turn swings it from edge-on (open) to square across the pipe (closed), where its rim presses into a resilient rubber liner molded into the body. The body is a thin ring that clamps between two flanges, so a 6 in. butterfly weighs a fraction of a 6 in. gate valve and costs a fraction as much.
Isolation on large lines, roughly 3 in. and up, where a gate valve would be heavy, tall and expensive: raw water and feed mains, filter and softener vessel isolation on big pretreatment trains, tank inlets and drains, municipal plant piping. It can also throttle coarsely, which a gate or ball valve cannot.
Municipal and industrial BWRO feed and concentrate headers, containerized RO skid inlet and outlet, backwash and rinse lines on large multimedia filters, tank farm manifolds. Wafer style sits between two flanges; lug style bolts to each flange independently so you can pull the downstream pipe with the line still charged.
Handle position tells you the disc position: parallel to the pipe is open. Anything 8 in. and larger usually has a gear operator instead of a lever, and the indicator on top is the only visual you get. Never use a wafer-style butterfly as a dead-end shutoff with the downstream pipe removed; only lug style is rated for that.
A flexible membrane (EPDM, PTFE-faced or similar) is pressed down by a compressor until it seals against a raised weir in the body. The membrane also seals the bonnet, so the stem, spring and actuator never touch the fluid. That isolation from the process is why it is the standard choice for aggressive chemicals and for clean or sanitary service.
Chemical feed and transfer: sodium hypochlorite, caustic, acid, antiscalant, coagulant. Membrane clean-in-place skids. Food and beverage lines where a smooth, crevice-free wetted path matters. It also throttles reasonably well for moderate control duty.
Chemical dosing panels and drum manifolds, CIP skids, food-plant process water, and as pneumatically actuated on/off valves for RO permeate divert, flush and CIP isolation on larger skids.
Weir type is the common one and handles throttling. Straight-through (full bore) diaphragm valves exist for slurries and drainage where the weir would collect solids. Know which one is in your hand before ordering a replacement diaphragm.
When you are specifying a replacement or laying out a new manifold, run down this table before you reach for whatever is on the truck.
| Valve | Isolation | Throttling | Pressure drop, open | Speed | Typical service at Axis |
|---|---|---|---|---|---|
| Gate | Yes | No | Very low | Slow | Well heads, mains, large tank isolation |
| Globe | Acceptable | Yes | High | Slow | RO concentrate control, pump throttling, balancing |
| Needle | No | Yes, fine | Very high | Very slow | Gauge lines, sample ports, chemical tuning, small RO reject |
| Ball | Yes | No | Very low (full port) | Fast | Bypasses, skid isolation, drains, quick-disconnects |
| Butterfly | Yes | Coarse | Low | Fast / geared | Large mains, vessel and tank isolation, filter backwash lines |
| Diaphragm | Yes | Moderate | Moderate | Medium / actuated | Chemical feed, CIP, sanitary, RO divert and flush |
One-way flow, no handle. Keeps pump discharge from draining back, keeps chemical from siphoning into the drum. Spring, swing or ball style. Fails by sticking open; listen for backflow on shutdown.
Electrically operated on/off, usually a small diaphragm or piston inside. RO inlet, permeate flush, drain valves on filters. Needs clean water and a minimum pressure differential; buzzing means it is not fully seating.
Spring-loaded diaphragm that holds a set downstream pressure regardless of inlet. Ahead of residential RO and softeners where city pressure exceeds 80 PSI. Set it with a gauge downstream, not by feel.
Ball, gate and butterfly valves are switches. Globe, needle and diaphragm valves are dials. Use a switch as a dial and you will be back to replace it.
