Sourcing RV and Camper Fittings From China: Water Pumps, Tank Interfaces and Inverters That Do Not Survive a Cold Night

RVs are a hostile environment pretending to be a leisure product. Every component sees continuous road vibration, a temperature range from minus 15 °C in a mountain pass to 60 °C inside a closed van in summer, a 12 V supply that sags hard during engine crank, and a water system that gets drained and refilled every few weeks. Components designed for domestic plumbing or household electronics fall apart in this environment, and they fall apart at the customer, three countries away, which is the worst possible place.

Water pumps: diaphragm, not impeller

Almost all decent caravan water systems use a self-priming diaphragm pump with an integrated pressure switch. The reason is dry running — a diaphragm pump tolerates running briefly without water, an impeller pump does not, and the first time a customer forgets to open a valve is the day you find out which one you specified.

What to check. Flow at 2.5 to 3 bar for a typical two-outlet installation, usually 10 to 15 litres per minute; but demand the flow-pressure curve, because a pump rated 15 l/min at zero head will deliver far less once it is pushing through a filter and a 6 metre run of 10 mm pipe. The pressure switch cut-out should be adjustable and matched to the accumulator you specify, and the pump must be rated for continuous duty, not intermittent — the datasheet will say "continuous" or "30 min on / 30 min off" and the difference matters when someone showers.

Diaphragm material is the failure point. EPDM or santoprene handles potable water well; cheap nitrile does not, and it will leave a taste. Demand a potable water certificate — in Europe that is typically a WRAS or DVGW approval, in the US NSF/ANSI 372 for lead-free and NSF/ANSI 61 for contact. If the supplier cannot produce one for the exact model, do not buy it for a drinking water system, full stop.

Also check the check valves inside the pump head. A pump that runs for a second every ten minutes at night is a leaking internal check valve, and it is the number one noise complaint on a campsite. Ask for the valve material and whether the pump has a bypass or a pressure switch with hysteresis wide enough to tolerate small leaks.

Tank interfaces: the fittings nobody specifies

The tank itself is usually rotationally moulded HDPE and rarely the problem. The fittings are. Threads on a moulded tank are imprecise by nature, and a hard-threaded fitting over-tightened into a soft plastic boss will crack, sometimes immediately, often six months later.

Best practice is a bulkhead fitting with an elastomer gasket on both sides of the wall, clamped rather than threaded into the wall, and a generous flat land moulded into the tank. Specify the boss dimensions and the wall thickness with tolerance, because a 20 percent variation in wall thickness changes the clamping behaviour entirely. And check that the gasket material is compatible with whatever the customer might put in the tank — some winterising fluids and sanitising agents attack EPDM.

Level sensors are their own small nightmare. Float switches are cheap and reliable but stick; capacitive sensors avoid moving parts but drift with water conductivity and condensation. If you are specifying a capacitive sensor, get a unit with a temperature compensation and a stated accuracy over a conductivity range, not a single "% full" figure.

Inverters: the 12 V problem

A campervan inverter lives on a cable run from a battery that may be 3 metres away, at 12 V, delivering 2,000 W. That is 170 A at nominal voltage, and close to 200 A when the battery sags. Cable and fuse sizing are where installations fail, and this should be in your installation manual, not left to the fitter.

On the inverter itself, ask for pure sine wave output and a THD figure at rated load — some units quote THD at half load because it flatters the number. Check the surge rating and how long it lasts; a compressor fridge or an induction hob start can draw double rated power for a second or more. Check the low-voltage disconnect point and whether it is adjustable, because a lead-acid bank and a lithium bank want very different thresholds, and the wrong setting either strands the user with a dead battery or disconnects far too early.

The idle current draw matters more than people expect. An inverter left on overnight at 1 A constant draw takes 24 Ah out of the bank doing nothing. Under 0.5 A at no load, ideally with a real power-saving search mode, is what I look for.

And charging compatibility, if you are selling a system: a lithium iron phosphate bank needs a charger and a solar controller with an adjustable absorption voltage and no equalisation cycle. A drop-in lead-acid replacement profile will charge a LiFePO4 bank to 80 percent and call it done, or worse, hold it high and shorten its life.

Price expectations and the cold-soak test

A 12 l/min diaphragm pump at reasonable quality runs around USD 15 to 25 FOB at a few thousand units. A 2,000 W pure sine inverter is roughly USD 90 to 140 depending on certification and brand of the power devices. If a quote comes in 40 percent under those, the difference is usually in the switching devices and the magnetics, and you will find it out at full load in a hot van.

My standing requirement for any RV component is a cold-soak test: operate the unit at minus 15 °C for 8 hours and then bring it to rated load. Water pumps lose priming, plastic housings crack, LCD panels in control units go sluggish, and inverter capacitors behave differently. A supplier who has done this test will tell you about the failures. A supplier who has not will ask what you mean, and that answer is worth more than the quote.