Irrigation
RAIN LING Automatic Drain Valve
RAIN LING's automatic drain valve empties standing water from irrigation lines once pressure falls. Mounted vertically, it opens at 0.2 bar and closes again at 0.4 bar. RAIN LING presents it as a way to protect pipes from damage and frost, and describes it as corrosion-resistant, self-cleaning and maintenance-free. Fit it at low points where water collects after shutdown. Before you rely on it for winter, check the pressure left in the line after the pump stops, plan where the water goes, and ask RAIN LING for the thread size, drain flow and closed-state pressure rating.
Lingxing Irrigation Technology (Ningbo) — RAIN LING ↗
Build my procurement briefOpening and closing points
RAIN LING gives one pressure for opening and another for closing, both for vertical mounting. Treat them as two separate switch points of one cycle.
| What RAIN LING states | What to ask |
|---|---|
| Opens at 0.2 bar | The valve opens as line pressure falls to this level. Ask for the tolerance band, the drain-flow curve and the pressure reference point. |
| Closes at 0.4 bar | The valve shuts as pressure rises past this level. Ask for the closed valve's maximum working pressure and leak-test figure. |
| Vertical installation | Both values apply when the valve is mounted vertically. Ask about any other orientation before planning it. |
| Between 0.2 and 0.4 bar | Ask how the valve behaves in this band, for example whether it stays in its last state. |
Sources [1]
Pump off is not zero pressure
The valve responds to pressure at its own position. When the pump stops, water standing higher up the line can still press on the valve. Elevation, the supply arrangement and any check or isolation valves all affect what pressure remains.
UF/IFAS describes static head as the pressure that comes from height. As a rough guide, a 2 m column of fresh water (density 1000 kg/m³, gravity 9.81 m/s²) gives about 0.196 bar, close to the 0.2 bar opening point. So a few metres of water above the valve can be enough to matter.
Send RAIN LING your elevations and line arrangement, and ask for the valve's switching and drain response under that remaining head. Where a pump feeds the line, our guide to choosing a petrol engine water pump explains total head, which rests on the same height-to-pressure idea.
Published specifications
Read each value with its stated conditions, and ask the manufacturer for any limit not listed here.
| Specification | Published value | Meaning / limit |
|---|---|---|
| Opening / closing pressure | 0.2 bar opening / 0.4 bar closing [1] | Stated for vertical installation. Ask for tolerances and where the pressure is measured. |
| Function | Releases accumulated line water when pressure drops below the preset level [1] [4] [6] | Drain time and leftover water depend on your layout. Ask for a drain-flow curve. |
| Body | Threaded body, perforated face and reverse view [2] [3] | Photos carry no model or size label. Ask for the code, thread standard and dimensions. |
| Working limits | Maximum pressure, temperature, media and drain capacity to request [1] [2] [3] | 0.4 bar is where the valve shuts. Ask separately for the highest pressure the closed valve withstands. |
| Service claims | Corrosion resistance, self-cleaning and maintenance-free design described by RAIN LING [1] [3] | Ask for the material and seal list and any inspection interval for your water quality. |
Where the water goes, and letting air in
The drain valve releases standing water at low pressure. RAIN LING's air-release valve is a separate product that lets trapped air out and helps prevent vacuum. A line usually drains faster when air can enter at the high points, so ask whether your layout needs both.
Mark the low points, sections cut off by other valves and the route the drained water will take. Water held behind other components or in sections that cannot reach the drain point will stay in the pipe. If those components include EVA/EVD solenoid valves, note which side of each valve the drain sits on. RAIN LING's farm and greenhouse photos show typical markets.
Ask RAIN LING for the drain curve and its conditions, how many valves it recommends for your pipe length and volume, and the flow through the drain holes.
Connection and service details
The photos show a black threaded body with a perforated face and a view of the reverse side. Use them to identify the part, then get the measured data below.
| What the photos show | What to request for your order |
|---|---|
| Threaded body | Order code, nominal size, thread and seal standard, overall size and mounting drawing. |
| Perforated face | Drain flow at a stated pressure and head, and outlet arrangement. The photo shows seven holes; ask for the rated discharge. |
| Reverse side | Material, seal and assembly list and current service instructions. |
| Closed duty | Maximum working and surge pressure, temperature, water quality and leak rate for this valve. Other RAIN LING valves carry their own limits. |
| Self-cleaning and maintenance-free | Inspection conditions for your water quality, and spare-part support. |
Checking frost protection on your layout
RAIN LING says removing standing water helps prevent pipe and frost damage. What matters is whether your planned arrangement empties the sections you care about when the system shuts down. Other makers' drain and air valves can be compared in our irrigation category.
Describe the layout
Pipe route, supply and isolation, remaining head, drain orientation and where water discharges.
Get the part data
Model and thread, switch-point reference and tolerances, drain curve and closed-state limits.
Test a shutdown
Shut down a representative section, record remaining pressure and check how much water drains out.
Keep the paperwork
Installation and service instructions, any winterisation guidance and replacement and support terms.
Buyer questions
Is 0.4 bar the maximum working pressure?
No. It is the closing point. Ask RAIN LING for the closed valve's maximum and surge pressure. [1]
Do the pressures apply in any orientation?
RAIN LING states them for vertical installation. Ask before mounting it any other way. [1]
Will every section drain once the pump stops?
Only if pressure at the valve falls to 0.2 bar and the water has a path to it. Height above the valve and closed sections can hold water back. [1] [6]
Prepare a model-specific brief
Write your actual conditions below. This local worksheet is not sent, uploaded or saved after reload. Copy or print it before leaving.
Sources
Specifications come from the manufacturer's publications listed below, with the date each was checked.
- RAIN LING official automatic-drain valve description
manufacturer · Checked 2026-10-12
Opens at 0.2 bar and closes at 0.4 bar when vertical; drains standing water to limit pipe and frost damage; self-cleaning and maintenance-free design.
- Original front and reverse drain-valve views
manufacturer · Checked 2026-10-12
Perforated face, threaded body and reverse face.
- Original reverse-side close view
manufacturer · Checked 2026-10-12
Close view of the reverse side of the valve.
- Original agricultural/greenhouse application illustration
manufacturer · Checked 2026-10-12
Park, farm, greenhouse and horticultural irrigation scenes.
- Official air-release page
manufacturer · Checked 2026-10-12
RAIN LING's separate air-release valve for trapped air and vacuum.
- UF/IFAS Cir1425: static pressure and elevation
official disclosure · Checked 2026-10-12
Pages 1–4 explain how elevation creates static head and how it differs from operating pressure.
Report a correction through our contact form, quoting RAIN LING Automatic Drain Valve and the relevant specification.