An ejector condenser is a contact-type steam condenser that uses a jet of cold injection water — accelerated through a converging nozzle — to entrain, condense, and discharge exhaust steam in a single combined stream, eliminating the need for a separate air pump. The arrangement was patented and commercialised by Morrison in the 1870s. The kinetic energy of the injection jet drags the mixed condensate, air, and uncondensed steam down through a tail pipe and out against atmospheric pressure. The result is a compact condenser that creates 24–26 inHg vacuum and self-discharges its hotwell, widely used in marine auxiliaries and small mill engines.
Ejector Condenser Interactive Calculator
Vary steam load, injection ratio, jet velocity, and tail-pipe head to size the injection-water flow and nozzle throat.
Equation Used
The calculator applies the ejector condenser sizing relationship described in the article: choose a water-to-steam injection ratio, convert the required injection-water mass flow to volume flow, then size the nozzle throat area from the selected jet velocity. The 34 ft barometric leg check shows whether the tail pipe has the minimum effective head to discharge against atmosphere.
- Water density is 62.4 lb/ft3.
- Jet velocity is the actual nozzle exit velocity, not ideal pressure velocity.
- Direct-contact condensation uses the selected water-to-steam mass ratio.
- A 34 ft barometric leg is the minimum discharge head reference.
How the Ejector Condenser Works
The ejector condenser works on momentum transfer. Cold injection water enters the head at 10–20 psi, passes through an annular converging nozzle, and accelerates to roughly 30–50 ft/s as it crosses the steam-admission belt. Exhaust steam from the engine enters that same belt at near-atmospheric or slight-vacuum conditions and meets the high-velocity water curtain. Direct contact collapses the steam almost instantaneously — latent heat dumps into the water in milliseconds — and the combined stream carries entrained air and any uncondensed vapour down the tail pipe. The whole device replaces the jet condenser plus separate air pump found on a typical Edwards or Weiss installation.
Geometry decides whether you get vacuum or a wet mess. The throat diameter, the nozzle-to-tail-pipe gap, and the tail pipe length must match the rated steam flow. If the injection ratio drops below about 25 lb of water per lb of steam, condensation goes incomplete and the tail pipe slugs — you hear it banging and the engine vacuum collapses to 10–12 inHg. Push the ratio above 50:1 and you waste injection-pump power and overheat the hotwell. The tail pipe itself must be at least 34 ft of effective head — the barometric leg — or it cannot discharge against atmosphere when vacuum is present.
Failure modes are predictable. Scale build-up in the nozzle throat narrows the jet, drops velocity, and kills entrainment — you'll see vacuum fall over weeks of running on hard water. Air leaks anywhere in the exhaust line above the water seal flood the condenser with non-condensables that the jet cannot fully entrain, and the vacuum gauge will hunt by 2–3 inHg. A cracked tail pipe joint admits atmospheric air directly into the throat and the condenser stops pulling vacuum entirely.
Key Components
- Injection water nozzle: Converging annular nozzle that accelerates the cooling water to 30–50 ft/s. Throat diameter is typically 0.75–1.5 inches on small marine units and is sized for rated steam mass flow at a 30:1 water-to-steam ratio. Bore tolerance matters — 0.5 mm of scale on a 20 mm throat costs you 5% of jet velocity.
- Steam admission belt: Annular chamber surrounding the nozzle exit where exhaust steam meets the water curtain. Cross-sectional area must keep steam velocity below 200 ft/s to avoid choking the jet. Connects directly to the engine exhaust pipe with a short, large-radius elbow.
- Mixing cone (combining throat): Short converging section downstream of the steam belt where condensation completes and the mixed flow accelerates. Length is usually 4–6 throat diameters. Wear of the cone bore by erosion shows as a gradual loss of vacuum over thousands of running hours.
- Tail pipe (barometric leg): Vertical discharge pipe that must exceed 34 ft effective height to balance atmospheric pressure against full condenser vacuum. Internal diameter is sized for 6–10 ft/s discharge velocity. Any horizontal run breaks the seal and lets air back into the condenser.
- Hotwell / discharge seal: Receives the warm condensate and injection water mixture at the foot of the tail pipe. Maintains a water seal against atmosphere — depth of 6–12 inches below the tail pipe outlet is standard. Overflow is gravity-fed to drain or to feedwater service.
- Snifter valve: Small non-return valve on the steam belt that releases trapped air during start-up before vacuum forms. Without it, the condenser cannot prime — the injection jet stalls against a column of compressed air on first run.
Industries That Rely on the Ejector Condenser
Ejector condensers earned their place wherever a designer wanted vacuum without the bulk and maintenance of a reciprocating air pump. They show up in marine auxiliary plant, small mill engines, traction engines fitted for closed-cycle running, and sugar-mill vacuum pans. The compactness and absence of moving parts make them attractive for installations where deck space, weight, or simplicity matter more than absolute thermal efficiency.
- Marine auxiliaries: Auxiliary condensers on coastal steamers and steam yachts — the Morrison ejector condenser was standard fitment on numerous late-19th-century Clyde-built vessels for auxiliary engine exhaust.
- Sugar processing: Vacuum-pan condensers at sugar refineries such as Tate & Lyle's Plaistow Wharf works, where ejector condensers pulled vacuum on evaporator effects without separate air-pump trains.
- Heritage steam preservation: Recommissioned launch engines at the Windermere Jetty Museum running closed-cycle on lake water through ejector condensers to give a 22 inHg vacuum on the low-pressure side.
- Stationary mill engines: Small textile-mill engines in Lancashire used Morrison-type ejector condensers as a cheap alternative to surface condenser plus Edwards air pump installations.
- Steam locomotive testing plants: Some early stationary test plants, including arrangements at Swindon Works, used ejector condensers on exhaust steam to allow closed-cycle measurement of steam consumption.
- Power station auxiliaries: Gland steam and drain condensers on early Parsons turbine installations used small ejector condensers to handle bleed-off steam from labyrinth glands.
The Formula Behind the Ejector Condenser
The defining calculation for an ejector condenser is the injection water mass flow required to condense a given exhaust steam mass flow and bring the mixture to a target hotwell temperature. At the low end of the typical ratio range — around 20 lb water per lb steam — you barely condense the exhaust and the hotwell runs near boiling, vacuum is poor, and the tail pipe slugs. At the high end — 50:1 or above — you waste pump horsepower and the injection pump becomes the dominant parasitic load. The sweet spot for most marine and small mill installations is 28–35:1, giving 24–26 inHg vacuum with a hotwell at 110–120°F.
Variables
| Symbol | Meaning | Unit (SI) | Unit (Imperial) |
|---|---|---|---|
| mw | Required injection water mass flow | kg/s | lb/h |
| ms | Exhaust steam mass flow into the condenser | kg/s | lb/h |
| hs | Specific enthalpy of incoming exhaust steam | kJ/kg | BTU/lb |
| hw2 | Specific enthalpy of mixed hotwell discharge | kJ/kg | BTU/lb |
| cp | Specific heat of injection water | kJ/(kg·K) | BTU/(lb·°F) |
| Tw1 | Injection water inlet temperature | °C | °F |
| Tw2 | Mixed hotwell discharge temperature | °C | °F |
Worked Example: Ejector Condenser in a recommissioned Edwardian steam launch on Lake Windermere
Sizing the injection water flow for a Morrison-pattern ejector condenser being fitted to a recommissioned 1908 Brooke compound launch engine on a 32 ft steam launch operating out of the Windermere Jetty Museum boatshed. The engine exhausts 480 lb/h of steam at 5 psi back-pressure (hs ≈ 1156 BTU/lb), drawing injection water from the lake at 52°F. Target hotwell discharge is 115°F to maintain 25 inHg vacuum.
Given
- ms = 480 lb/h
- hs = 1156 BTU/lb
- Tw1 = 52 °F
- Tw2 = 115 °F
- cp = 1.0 BTU/(lb·°F)
- hw2 = 83 BTU/lb (water at 115°F)
Solution
Step 1 — heat to be removed per pound of steam, from incoming exhaust enthalpy down to hotwell enthalpy:
Step 2 — at the nominal target hotwell temperature of 115°F, compute injection water mass flow:
That works out to a water-to-steam ratio of 8175 / 480 ≈ 17:1 — uncomfortably lean. The lake supplies cold injection water (52°F is genuinely cold) so the temperature rise can be larger than typical, but a 17:1 ratio is at the edge of slugging behaviour. Step 3 — re-run at the high end of typical practice with hotwell at 100°F (cooler discharge, more vacuum margin):
That gives a 22.7:1 ratio and a comfortable 26 inHg vacuum target. Step 4 — at the low end, a hotwell at 130°F (lazy injection pump, hot summer day on the lake):
At 6500 lb/h you'd be at a 13.6:1 ratio — the tail pipe will hammer audibly, vacuum will collapse to under 18 inHg, and the engine indicator card will show a lifted exhaust line. The practical sweet spot for this launch is sizing the injection pump for around 11,000 lb/h with a manual throttle, letting the operator trim ratio against measured vacuum.
Result
Nominal injection water flow comes out at 8175 lb/h to hold a 115°F hotwell on 480 lb/h of exhaust steam. In practice that means an injection pump rated for roughly 16 USGPM at 15 psi delivery — a small belt-driven centrifugal off the engine crankshaft handles it comfortably. Sized lean at 6500 lb/h the condenser slugs and vacuum collapses; sized fat at 11,000 lb/h you get rock-steady 26 inHg vacuum at the cost of an extra 0.5 IHP driving the injection pump. If you measure 20 inHg instead of the predicted 25 inHg, the three usual culprits are: (1) air leak at the snifter valve seat letting non-condensables into the steam belt, (2) tail pipe shorter than 34 ft effective head — common when the condenser is mounted too low in the hull, or (3) injection nozzle partially blocked by lake-weed debris, dropping jet velocity below the entrainment threshold.
When to Use a Ejector Condenser and When Not To
An ejector condenser is one of three plausible answers when you need vacuum on a small-to-medium steam plant. The other two are a jet condenser with a separate air pump (Edwards or Weiss type) and a surface condenser with feedwater recovery. Each suits a different priority — simplicity, efficiency, or feedwater purity.
| Property | Ejector Condenser | Jet Condenser + Edwards Air Pump | Surface Condenser |
|---|---|---|---|
| Achievable vacuum (inHg) | 24–26 | 26–28 | 28–29.5 |
| Moving parts in condenser | Zero | Air pump piston, valves, eccentric drive | Tubes plus circulating and extraction pumps |
| Typical injection ratio (water:steam) | 25–35:1 | 20–30:1 | 50–80:1 (cooling water, no contact) |
| Feedwater recovery | None — condensate mixes with injection water | None — same contact mixing | Full — clean condensate returns to feed |
| Capital cost (relative) | 1.0× | 1.6× | 3–5× |
| Footprint and weight | Compact, lightest | Medium — air pump adds bulk | Largest — tube nest plus pumps |
| Best application fit | Small marine and mill engines, vacuum-pan service | Mid-size mill engines wanting better vacuum | Large stationary plant, all closed-feed installations |
| Maintenance interval | Annual nozzle descale | Quarterly air-pump valve inspection | Annual tube cleaning + pump overhaul |
Frequently Asked Questions About Ejector Condenser
This pattern points almost always to thermal expansion opening a joint that was tight cold. The steam belt and the cast head expand at different rates from the steel tail pipe flange — by the time the casting reaches 180°F a poorly bedded gasket can lift 0.002–0.005 inches and start admitting air.
Run the engine until vacuum settles, then do a soap-bubble test around every flange on the suction side. The other candidate is the snifter valve disc not re-seating fully when warm — pull it and check the seat for a clean, continuous contact ring.
Textbook ratios assume the injection water enters at 60–65°F and the hotwell is allowed to discharge at 100–110°F. If your injection source is warmer than 65°F — common in summer on a closed cooling pond — the available temperature rise shrinks and you need proportionally more water to absorb the same latent heat.
Check actual injection inlet temperature with a thermometer in the supply line, not from a chart. A 10°F warmer source typically pushes the required ratio up by 15–20%.
For a 25 IHP launch the ejector condenser wins on weight, cost, and the absence of an air-pump drive off the crankshaft. You give up roughly 2 inHg of attainable vacuum, which on a small compound engine costs about 3–4% of indicated power.
If the boat is a day launch where simplicity matters and you have generous injection water from the lake or river, the ejector is the right answer. If you're chasing maximum efficiency on a long-distance steamer where coal economy dominates, the Edwards pump arrangement pays back its complexity.
Hammering at an apparently correct ratio almost always means the steam and water are not mixing in the right place. Either the nozzle-to-throat gap has drifted from spec — usually because someone re-machined a worn nozzle and didn't preserve the original axial setback — or the steam admission belt is choking because the exhaust pipe area is undersized.
Measure the gap between nozzle exit and throat entry; it should be 0.5–0.75 throat diameters on a Morrison-pattern unit. A gap below 0.3 diameters causes the jet to impinge on the throat wall and break up before it has entrained the steam.
Yes, and ejector condensers historically did exactly that on harbour craft and pinnaces. The contact mixing means there are no tubes to scale up — the only scale-prone parts are the nozzle bore and the mixing throat. Inspect both annually and de-scale with a 5% sulphamic acid soak.
The bigger consequence of seawater injection is that you cannot recover any of the condensate as feedwater. You'll need a fully independent boiler feed source and a hotwell that overboards the saline mixture rather than returning it.
The 34 ft figure is the barometric column height needed to balance one atmosphere of pressure differential at full vacuum. With only 28 ft of leg you'll never sustain better than about 24.7 inHg vacuum because the water column cannot support more — at higher vacuum the leg simply breaks suction and air rushes back up the pipe.
If 28 ft is your hard ceiling, accept that as the design vacuum and re-rate the engine accordingly, or fit a small extraction pump at the foot of the tail pipe to make up the missing head. The pump only needs to handle the discharge flow, not generate vacuum itself.
References & Further Reading
- Wikipedia contributors. Surface condenser. Wikipedia
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