Trustpilot rating stars4.5 ★
Toggle Nav
My Cart
Search
Advanced Search
  • Compare
Menu
Account
main product photo
Visit DeWalt Brand Store
dewalt

5140043-78 O-Ring - Dewalt

Be the first to review this product
$6.32
In Stock
SKU
5140043-78
test test
ⓘKnow Before You Order
×

Know Before You Order

Some orders ship faster than others

We stock tens of thousands of parts in our warehouse, and most in-stock orders ship within 24 business hours. Because we specialize in hard-to-find tool parts, some items are sourced directly from the manufacturer after your order is placed and may require 10–14 business days before shipment. We believe in being transparent about timelines so you know what to expect before ordering. If timing is critical, please contact with your part number for an estimated delivery timeframe.

Why does M&M Tool Parts offer parts other companies don’t?

As a family-owned business, we’ve built long-standing relationships with trusted manufacturers across the industry. These partnerships allow us to source specialty parts that are often unavailable through larger retailers or online marketplaces. In many cases, M&M Tool Parts provides one of the few reliable ways to obtain these components — and we work hard to get them to you as quickly as possible.

What should I expect after placing my order?

Our team begins processing orders immediately. If your item is stocked locally, you’ll typically receive tracking information within 24 business hours. For manufacturer-sourced items, we coordinate directly with vendors to secure and ship your order as efficiently as possible. We understand downtime is frustrating, and we sincerely appreciate your patience while we help source parts that can often be difficult to find elsewhere.

This DeWalt 5140043-78 O-Ring is a genuine OEM replacement sealing component used in the pump assemblies of compatible DeWalt and legacy pressure washers.
Read More

The DeWalt 5140043-78 O-Ring is a genuine OEM replacement sealing component used within the pump assemblies of compatible DeWalt and legacy pressure washers. Manufacturer parts documentation identifies 5140043-78 simply as “O-RING.” Its exact position and quantity vary depending on the pressure washer and pump configuration.

Product Specifications

Part Number: 5140043-78
Part Type: O-Ring
Manufacturer: DeWalt / DeVilbiss
Manufacturer Description: O-RING
Application: Pressure Washer Pump Assembly
Condition: Genuine OEM Replacement Part

Tool Compatibility

DeWalt 5140043-78 is documented for compatible pressure washer configurations including:

DeWalt DH4240 – Applicable Configurations
DeWalt DP3100 – Type 2
DeWalt DP3100IC – Type 2
DeWalt DP3700 – Applicable Configurations
DeWalt DP3850 – Applicable Configurations
DeWalt DPD3000IC – Type 1
DeWalt DPD3100IC – Type 1
DeWalt DPD3300 – Type 1
DeWalt DPD3800 – Applicable Configurations
DeWalt DPE3800 – Applicable Configurations
DeWalt DPE3800X – Applicable Configurations
DeWalt DPH3800 – Applicable Configurations

Part number 5140043-78 is also documented for the legacy DeVilbiss / Black & Decker BDP2600 pressure washer platform. Verify the complete model, type, and pump configuration against the applicable parts diagram before ordering.

Part Function

The 5140043-78 O-Ring provides a seal between mating components within the applicable pressure washer pump assembly. Its exact installation location varies by pump design, so the O-ring should be matched by part number rather than appearance alone.

Important Quantity and Compatibility Information

Some pressure washer pump assemblies use more than one 5140043-78 O-Ring. For example, the DeWalt DP3100 Type 2 and DPD3300 Type 1 parts diagrams specify two 5140043-78 O-rings in the unloader assembly, positioned with the 5140043-77 Retainer and 5140043-79 Piston Assembly. Other pump configurations use a different quantity or position.

Do not assume that every 5140043-series unloader component fits every pressure washer that uses the 5140043-78 O-Ring. This O-ring was carried forward into additional pump designs that use different surrounding components. Always verify the exact pressure washer model, type, and pump breakdown before ordering.

Related Unloader Components

5140043-77: Retainer
5140043-79: Piston Assembly
5140043-80: Stem
P776 / CAT 46250: Washer
5140043-81: Valve Retainer
5140043-82: Seat
5140043-83: Valve

Related components are sold separately unless specifically stated otherwise.

More Information
On OfferNo
Buy TogetherNo
Ship FreeNo
Write Your Own Review
You're reviewing:5140043-78 O-Ring - Dewalt
Compatibility
  1. DeWalt DH4240 Type 0 Parts - Pressure Washer
  2. DeWalt DP3100 Type 2 Parts - Pressure Washer
  3. DeWalt DP3700 Type 2 Parts - Pressure Washer
  4. DeWalt DP3850 Type 1 Parts - Pressure Washer
  5. DeWalt DPD3300 Type 1 Parts - Pressure Washer
  6. DeWalt DPD3800 Type 1 Parts - Pressure Washer
© Copyright 2026. MMToolParts.com All Rights Reserved.