SWEP B35

Flow and controls first, glycol second. An evaporator freezes when water flow drops while the refrigerant side keeps pulling the plate surface below freezing, and it happens in seconds. Water freezing in the channels can split the unit, after which refrigerant and water mix.

Prove water flow with a flow switch before the compressor is allowed to start, set the low-pressure cutout so the evaporating temperature cannot sit below the freezing point of the fluid, and let the pump run on after the compressor stops. Where leaving temperatures are near freezing, use glycol and select the unit on that mix. Freeze Protection goes through the interlocks.

SWEP lists threaded, Victaulic, solder, flange and O-ring connections on the frame. The builds on file are narrower: four 1 1/2 in connections, in a plain version and an NPT version. Those are different threads, and the suffix NPT on the designation is what tells them apart.

Forcing an NPT fitting onto a non-NPT thread is a common site error. It seals for a while and then weeps. If the existing pipework is grooved, soldered or flanged, specify that connection on the exchanger instead of adapting from a thread, because each adapter adds a joint, length and leverage on the port. State the joint type at all four ports with the request.

Because those are the configurations that happen to be catalogued, not the limit of the frame. The four builds on file are H-plate, single-pass units of 40, 50 and 60 plates. The frame itself goes to 251.

More plates lower the pressure drop and tighten the approach at a given flow, at the cost of depth and weight - 5.91 kg plus 0.34 kg per plate, so about 26 kg (58 lb) at 60 plates. If a duty needs many more plates than the catalogued builds, give us the flows and temperatures and the count will be selected to suit.

It is a wide-plate general-duty frame: 243 mm across on a 393 mm plate, which gives large ports for the height. That suits high flow with a moderate temperature change - oil cooling, condenser water, process loops - in a short package.

The short plate is also its limit. Where a duty needs a close approach or a large temperature change in one pass, a taller plate does it with fewer plates; on the B35 the answer is a two-pass build such as the published B35H/2P-SC-S, with the extra pressure drop that brings. The B35T shares the 393 x 243 mm plate at 118.88 GPM and is the model described for district heating, heat recovery and engine oil cooling.

It places the unit in the S pressure class, the 31 bar at 155 C category used for a wide variety of applications, and every B35 build on file is S class.

Read it as a category. The pressure and temperature that govern the installation, and the relief valve setting, are the ones stamped on the unit. Other classes exist on the same plate, so copy the letter from the old nameplate.

UL is the listing most US inspectors and insurers look for on a brazed plate exchanger in packaged equipment, and the B35 carries it alongside PED for Europe and KHK for Japan.

Some jurisdictions and owner specifications go further and require an ASME stamp, and Canadian work needs a CRN. Those are separate from the three published here and have their own temperature envelopes: -40 C to +150 C for ASME and -196 C to +225 C for CRN. Read the specification before ordering, because an approval cannot be added to a unit after it is built.

A strainer on each circuit that holds back anything near 1 mm, placed just upstream of the inlet. Oil circuits and process loops carry wear metal, gasket fragments and scale that a closed water loop does not.

On oil duty, check the strainer pressure loss at cold-start viscosity. A screen that is fine at operating temperature can starve the cooler when the oil is cold. Fit pressure tappings across the exchanger so a rising differential is seen early. Once debris is wedged in the channel entries of a brazed pack, back-flushing recovers only part of it, and the unit runs at reduced capacity from then on.

These models are catalogued alongside the B35. Each has its own page with its dimensions, materials and part numbers.

SWEP B35T - A wide copper-brazed plate heat exchanger for district heating, HVAC and oil cooling.